5.2.1. Land use planning context
Rural and urban land use planning literature shows significant context differences. Rural land use planning is mainly mainstreamed by ecosystem services within the general framework of sustainable development. This makes real-world problem representation more rational, detailed, and concrete to practically tangible problems level. On the contrary, urban land use planning problems have been formulated as general management-oriented problems. Another key difference is the extent to which the problem is established in accordance with relevant theories/concepts and the representation of reality. In all aspects, important knowledge can be transferred from rural land use planning literature to urban land use planning study. Nondeterminism, uncertainty, intertemporal span, and heterogeneity land uses that offer certain functions (ecosystem services) are crucial aspects of reality representation identified in the sampled papers. Brief description of each work and discussion follows.
Current state:
The temporal dimension makes land use optimization a spatiotemporal problem. Sdshu, et al (2008) optimized agricultural land allocation problems that maximize income from sheep and grouse farming activities. Five activities are available to choose different mixes under tenant farmer managers and landlord managers lland management options. The overall land management problem was reconciling the benefits of short-term tenant farmers’ benefits and long-term investment proprietors’ benefits. The short-termism tenant farmers were supposed to maximize their income on an annual basis whereas landlords seek medium to long-run investment returns. Whether land has to be managed by the tenant farmers or the landlord management each of which maximizes income adds temporal conflict to the conventional spatial problem. Under the tenant formers management, land use change is supposed to occur for every contract term, possibly every year. Under the landlord management, land use change would be determined by the cumulative return assessment for t-years. The land allocation problem of the tenant farmers that maximizes income would be evaluated for every single production cycle. Whereas that of the landlords, since a one-time solution solved under a static situation will not respond to comparing the benefits of short-termism and long-term, would be evaluated for a five-year period or 10-year intertemporal scenarios. The intertemporal model is a dynamic model that inputs dynamic variables (changing grouse population, grouse price, and government subsidy). Results demonstrated a strong correspondence between the length of management and stability of land use change (mixing of farming activities). Land use changed nine times after the subsidy reform under the temporal scenario which is not ideal for the proprietors. Under the five-year intertemporal scenario, 3-sheeps/hectare farming would turn well before the subsidy reform program ends. For the next 2-five years, land use would change seven times. Under the 10-year intertemporal scenario, 3-sheep/hectare would be profitable, and land use change would occur only once within 14 years. After the end of the subsidy program, grouse shooting would become a dominant activity accompanied by a more stable land use. The intertemporal models indicated the frequency of land use changes that respond to decision makers' and land managers’ understanding of how land use planning changes over a defined period. Nonetheless, the temporal component of optimal land use planning remains underrepresented because of the deterministic tradition.
Uncertainty programming enhances resource allocation rationality. Flexibility accommodates various aspects of unpredictable elements spanning inputs, processes, and output. The continuously changing land use structure involves spatiotemporal characteristics (Zhu et al., 2020) but the temporal dimension is addressed very weakly. Socioeconomic, biophysical, and biological factors cause changes. Such change parameters need to be captured periodically. Most spatial optimization models for sustainable land use planning are designed to answer which land parcels are used for what purpose (Yao et al., 2018) usually under static state assumption. At this point, one can think of transferring the temporal dimension associated with the accession and succession relation of businesses and households in the bid-rent land allocation theory. A corresponding practice can be referred to in timber harvest scheduling (Verburg, et al., 2002) which concerns spatial harvesting patterns over a multi-period time horizon (St. John & Tóth, 2015). Although the practice of uncertainty modeling is common in different environmental, ecological, and land use optimization research, Li & Ma (2017) argue previous works lacked a systematic approach to the determination of types and sources of uncertainties. They also claim that lack of transparent methods for the involvement of stakeholders in deciding objectives in the account that objective identification involves uncertain environment. In their own study, the authors modeled uncertainty within input parameters and output (objective function values). Input parameter values were simulated stochastically between the upper and lower demand targets (historical data and experts’ evaluations) under different significance level scenarios. For the output (objective function values), the range was constructed based on the 10,000 best solutions sampled from each run. The study by Li et al (2021) analyzed the spatiotemporal evolution of ESs in association with LULC changes. They optimized both ESs and economic benefits under business as usual, ecological priority, and balancing economy and ecology scenarios. They modeled the uncertainty of input parameters by applying the Gray Multi-objective Optimization programming (GMOP) and they simulated the spatial layout using Patch-generating Land Use Simulation (PLUS). First, the quantitative LULC was optimized to the target year. In the second stage, the spatial distribution was simulated applying the PLUS. Zhu, et al (2020) contributed to the uncertainty by considering the temporal element. The works of Wu, et al (2018) and Li, et al (2021) introduced uncertainty via gray value objectives and constraints. The intertemporal work of Jin, et al (2019) is another variant of uncertainty. The geometric progression element in the compensation determination in Liu, et al (2015) dynamic game model addresses the periodic oscillation of decisions of the parties where the action of one party is conditioned by the decision of the other party is another variant uncertainty modeling. The elements of uncertainty in the work by Wu et al (2018) are of two types. In their study of the effect of land use change over ecosystem service, they applied a range of input values and experts’ opinions based on multiple criteria to filter final solutions. In their land use optimization work, the objectives were water sustainability, water production sustainability, soil retention, carbon sequestration, and agricultural production evaluated for 6859 land unit scenarios (land units differing for slope grades/low, medium, and high; land use type/farm, forest, shrub, construction; and water constraint/ below minimum requirement, within minimum requirement range, above minimum requirement). An important value addition to the uncertainty in land use optimization is modeling uncertainty of stakeholders’ posteriori involvement via multi-criteria decisions to select planning options. The decision variables were the attainment of optimized objectives and the number of sub-watersheds that meet minimum water demand threshold for maintaining socio-economic activities. The authors did not use any tool for optimization. They simply assessed areas for target ESs using InVEST and Biophysical models. They found solutions for ecosystem service trade-offs in five scenarios. All scenarios improved each objective (Table-2). The importance of the study also lies in its demonstration of the importance of heterogeneity in land use policy for closing the magnitude of tradeoffs among ecosystem services and promoting a more rational sustainable development.
Unlike the regional land use planning problem, the urban land use planning problem has to respond to a multitude of theories governing land allocation behaviors that are more complex than the ecosystem service accounting in the regional land use planning. Although urban land use optimization problems are often formulated as general management problems where objectives are generic, some works address important urban land allocation theories and models. Ligmann-Zielinska et al (2008) developed a multiobjective optimization model that promotes a compact built environment. They promoted compaction by minimizing the distance of the new development sites from existing developed areas and minimizing open space development objectives and density-based design constraints that require a threshold for a certain use allocation in a neighborhood. Yang et al (2015) explicitly addressed residential location choice mode in optimal land use planning. The residential choice model is among the core concepts that explain spatial separation based on utility theory. Spatial separation degrades the quality of life (i.e. accessibility to work, medical care, shopping, and leisure facilities). In the work by Yang, et al (2015), Workers live in the old districts for facilities and commute to the new development areas for employment. As a response, the authors integrated workers’ residential area and land use models in which they maximized the quality of life of the workers and productivity of facilities in the new development area formulated as a WS problem. Their work demonstrated that the land use of a new development area can be utilized more effectively if the land use allocation decision is based on housing location behaviors. Wang et al (2022) built another important theory, transportation accessibility, into urban land use optimization along with compactness, compatibility, and suitability objectives. Transport characteristics were quantified by driving accessibility, cycling accessibility, and walking accessibility maps. The accessibility objective function measures the degree of match between land use type and transport characteristics. The NSGA-II implemented a control group (without an accessibility objective) and an experiment group, demonstrating the importance of accessibility making the optimal land use map compatible with existing development potential.
The land use planning context can be categorized into basic land use allocation theories/models and dynamics. In relative terms, the latter is getting more depth and breadth development. A shift has occurred from temporal to intertemporal perspective and from deterministic assumption to uncertainty accommodation in many forms (including input parameters and output scope, participation and interaction of parties/stakeholders), to capturing degree of uncertainty. The progress on the fundamental theoretical/conceptual models of land use allocation theories (and spatial morphology in urban) is limited.
Frontiers:
Regardless of such a few works, many of the concepts related to the land use allocation problem of the built environment have remained either immature, the breadth of application is narrow, or completely unaddressed. Furthermore, specification of certain objectives contradicts with the basic land allocation and morphological concepts. These points are potential frontier research issues briefly indicated in the next paragraphs.
One way or another, transportation is an integral part of land use planning. Mathematical models use origin-destination data to model accessibility (Boussauw and Witlox, 2009; Allen and Sanglier, 1981a,b; Anas, et al., 1997). This way of modeling accessibility in urban land use optimization is not visible, however. Instead, Wang, et al (2022) applied a geographic accessibility map based on driving, cycling, and walking. The origin-destination model requires explicit commuting time/distance and impedance whereas the input of Wang, et al (2022) was mobility service of given transport systems aggregated into a composite accessibility index map. In case neither the origin-destination distance or time nor the accessibility infrastructure data is readily available, spatial proximity among functional uses can be an alternative approach, in which accessibility maps can be created for each travel purpose and the map index value can be utilized as input. The composite accessibility computed at a neighborhood level for all destinations of purpose metric shall also serve as an alternative mechanism to resolve the deficiency of Euclidean distance-based accessibility. Furthermore, neighborhood-based accessibility is leverage to problems of inconsistent traffic analysis zone sizes. Finally, neighborhood-based accessibility is consistent with the mixed-use version of sustainable development (Jabareen, 2006; Sharimin, 2011).
While transport infrastructure remains a key spatial organization entity, spatial structure may be better predicted based on comprehensive factors. The logistic regression method and the minimum cumulative resistance (MCR) model that are common in regional land use planning research can be transferred to the built environment. Logistic regression can be utilized to construct a probability map of land use types across space based on change-driving factors and the MCR can be applied to fine-tune the spatial allocations of uses based on the degree of resistance from a defined source of planning elements such as high-density residential land, special protected uses, industrial establishments, etc. Travel behavior is another key element that needs addressing in the optimal allocation of land under a given spatial structure the outcome of which may reflect feedback to a modal assignment policy. Currently, travel behavior is detached not only from the optimization literature but also is not integrated into land use types in other traditional modeling. For better modeling of the built environment, the work of Yang, et al (2015) is a typical example of the introduction of behavioral characteristics. It can be extended to modeling behaviors in its broader dimensions of which travel behavior modeling may contribute another perspective to optimal land use planning. It can be extended to integrate different land use models into a unified model so as to minimize the consequences of spatial separation meaningfully.
Urban land use planning optimization literature seems growing but detached from critical land allocation and urban morphology theories. The scientific potential of land use planning that does not account for the fundamental land use allocation theories would obviously be less credible for application. Distribution of economic benefits, say land value, employment, and investment, etc. and therefore associated social benefits (access to employment, investment in local physical and social infrastructure) can be captured well if the bid-rent theory/economic geography/ is considered while mapping the spatial layout of land use activities. The macro-morphological structure of a city is crucial to the modal distribution of traffic (Bertaud, 2004) and modal assignment (Ashenafi, 2015) because of the significant population density variation from one place to another place. In this line, a recent case study by the authors of this manuscript demonstrated a significant accessibility performance variation attributed to the morphological structure of Mek’ele city along centralized-multicenter-decentralized spatial structures (Mehari and Genovese, 2023).
Regional land use planning accommodates relatively more frequent changes than urban land use planning. This is so because it is the major carrier of human socioeconomic activities and ESs. ESs can be altered among different uses relatively easily and regional land is the source of every development (construction) land that makes use conversion more frequent. Therefore, optimizing land use for the attainment of better ecosystem products is normative. The relatively fixed supply of urban land and long-lasting structures (buildings, physical infrastructures, and even societal fabrics) make land use change within the built environment relatively static. That is why much of land use planning is a simulation of expansion areas. However, it can be argued that the simulation of future expansion does not capture the overall land use, and by extension, the overall development of the city. While the simulation may remain essential for handling the expansion part, it seems feasible to conceive an alternative approach to the already developed part. The possible alternative could be optimizing the distribution of flow resources such as restructuring population density patterns and transport modal assignments to existing major morphological and functional structures and capabilities, which is a reversal of the conventional way that seeks spatial restructuring to attain certain objective tradeoffs. In some cases where the redevelopment project objective is considered, the existing built-up area appears as a restriction. Yet, sustainable urban development requires infill developments and the use of available resources such as mobility networks. In this respect, the direction of land use optimization can be shifted towards adjusting stocks such as distribution of population densities, creation of new service or employment points, balancing catchment areas, flattening land-value gradients, etc. The work of Yang and Bian (2004) dealt with the optimization of the spatial distribution of the population aiming for total car traffic distance and by Yang et al (2015) who optimized the distribution of workers based on the quality of life and productivity of amenities are examples that indicate the potential the research direction for allocating flows over given spatial layouts. It is crucial to underscore that flow resources allocation to existing land use could be a more reasonable planning approach than considering changing land use to respond to flow resources in the built environment.
Studies that evaluate the effectiveness/efficiency of the built environment are rare. Evaluation of existing land use plans objectively is lacking. Demonstrating new methods and models returning land use maps having a better objective value does not necessarily indicate that the city would perform at its optimal state supposed by the model. More importantly, how planning policies affect the land use structure is not fully captured by comparison of scenarios. Scenario analysis is simply a relative metric. Evaluating the performance of the built-up environment may allow policymakers to revisit their past trends and learn from them. Furthermore, it may allow them to correct the structure of the built environment either via their redevelopment programs or by consider compensatory programs in the expansion area.
We also encounter a situation where urban land use optimization contradicts the basic principles of a sustainable built environment. Compactness has been mainstreamed in two forms in the sustainable built environment discourse. In the conceptual realm, it is gyrated around minimizing sprawl and infill development for the efficient use of land resources. In this mainstreaming, attainments are increasing accessibility to services, enhancing social mix, energy use efficiency, reducing pollution rate, etc. In this original thought, many studies (Kenworthy et al. 1989; Simmonds and Coombe, 2000; Masnavi, 2000, Stead, et al., 2000; Reid et al. 2011; De Lara et al., 2013) demonstrate the positive contribution of the availability of services at the local scale and mixed-use development. The basic concept of the compact city can be either of high density, a mix of uses, or high intensity of use (Burton, 2000; Jabareen, 2006; Sharmin, 2011). The normative association of compactness and sustainability is mainstreamed by the size of the entire city as a function of the productivity of land (Jenks and Burgess, 2000; Jabareen, et al., 2006; Boussauw and Witlox, 2009; Sharmin, 2011; Al-Thani, et al., 2013; Anthony, et al., 2018). Nevertheless, the mathematical expression of compactness objective function in land use optimization problems overlaps with the second mainstreaming that claims consolidation of the same use to certain clusters (Aerts and Heuvelink, 2002; Aerts et al., 2003; Ligmann-Zielinska et al., 2008) the outcome of which is spatial differentiation and by no means emission from transport is minimized, walking and cycling or use of public transport is promoted, travel distance is shorten, ecological land is conserved, equitable access to social infrastructure and services is ensured, etc. (Mouratidis, 2019). In principle, the objectives of maximizing larger clusters /minimize number of clusters/, contradict the basic thought of compact development, which is one of the sustainability criteria. In theory, clustering of the same uses should promote spatial separation among purposes of travel thereby increasing travel cost (distance, time, out of pocket pay), energy consumption, pollution level, etc. it is also worth mentioning that no empirical work that demonstrates the relative advantages of clustering over mixed-use in terms of resource efficiency, accessibility, and social equity is available to support the large cluster objectives. Compactness/contiguity, number of clusters, cluster size, and a minimum number of cells of certain use objectives are also employed to restrict use conversion or preserve certain locations. In such a case, molding them as constraints may sound more rational. Otherwise, such imposition is a kind of setting certain spatial configurations out of the algorithm environment. In the work by (Liu et al., 2015), the additive parameter (land use suitability) declined for agriculture (by 2.5%) because of the preferential treatment of compactness by the applied operators. In that research, the sensitivity analysis challenged modeling shape-oriented objectives in combination with additive objectives. Compactness showed higher sensitivity to the distribution of weights than its suitability counterpart. In general, if clustering is admitted for a certain rationale, identification of the organizing planning elements must be clear rather than simply minimizing the number of clusters or maximizing the size of clusters for certain uses.
Another dimension of the conceptual level discussion can be whether certain shapes (contiguity and compactness) should be the result of satisfying aspatial objectives or spatial objectives have to be determined within the imposed shape.
Detailing objectives to the level it is in line with economic accounting units of analysis such as the monetary value of use conversion cost, the value of industrial products or services values, fairness of distribution of location value of land, or measurable social development indicators, social fabric integration in urban design, etc. in terms of accessibility is another frontier in urban land use planning research.
Rural land use is very rich in depth. Contents are detailed socioeconomic and eco-environmental variables probing to disaggregating variables into accounting items level. On the contrary, much of the land use optimization of the built environment dwells heavily on coarse indicators such as the GDP contribution of certain land use types or the magnitude of land use conversion, for instance in the work of (Cao, et al., 2012) instead of computing the actual monetary value associated with the conversion matrix.
In the huge accumulation of urban land use optimization research, what factors cause the land use change and their relative degree of influence are rarely studied. Monetary equivalence quantification of the built environment services introduced as objectives is almost nonexistent. This time, it is not known whether the reportedly significant improvement in compactness realizes significant fuel consumption or travel time reduction; the value of sound and air pollution from compatibility; the value of travel cost (time or monetary) reduction associated with attained accessibility; etc. Furthermore, there are no standard values that define a certain land use in relation to objective parameters. Conceptual models can be adopted with appropriate customizations from environmental modeling that are common in a broad array of ESs accounting.
5.2.2. Optimization method
Current status:
A review by Ding, et al (2021) that explored the development of GA on land use planning indicates the current state of the art is coupling and hybridization. This finding seems conclusive to a wide array of metaheuristic optimization methods. As reported in
Table 2 above, 15 of the 19 (78.95%) regular articles we examined applied two or three methods. The six review articles also show that majority of the papers they reviewed applied hybrid methods. The reasons for using two or more methods are two - scalability limitations (efficiency and effectiveness) of global optimizers and the view that disaggregated spatial allocation of activities from the planning activity. The reason for the independent treatment of planning demand for land for different activities and spatial outlay mapping of the activities is further justified by decision-makers of certain policy specificities at the local spatial scale.
The scalability limitation of metaheuristic global optimizers is a classic knowledge. With an emphasis placed on the application of GA, because it is the dominant implementation algorithm, it is needless to cite sources that the common approach to solving the efficiency problem has been replacing the standard operators with purpose-oriented operators. The work of Cao, et al (2011, 2012) are examples where they modified genetic operators acting on neighborhood windows and its boundary information is an effective way of maintaining diversity in the population and another (constraint steering) mutation to filter out infeasible solutions from the evolution process along the evolution process. Another interesting solution is simplex-LP Sadeghi et al. (2009) applied. Although linear programming is criticized for objectives scalarization requirement (Arthur & Nalle, 1997; Chuvieco, 1993; Sadeghi, Jalili, & Nikkami, 2009), the simplex method optimized land use in an area where the dynamic of water and energy supply was at stake along with environmental sensitivity and economic goals pressuring agricultural land without the need for aggregation of the two objectives. The maximum economic return and minimum soil loss were formulated as a multiple objectives simplex-LP implemented in ADBASE, which is capable of solving multiobjective problems. Compared to the existing state, gains were 18.62% economic benefits growth and 7.78% soil erosion reduction. The magnitude of associated land use change was a 93% increase in orchard land and a 50% decline in dry farmland. This paramount shifting of land uses indicates on one hand the ability of the simplex-LP method and on the other side the magnitude of planning inefficiency.
The dominant solution is in fact hybridization; and various forms are available. Handayanto et al (2017) applied a semi-parallel hybridization of PSO and GA further strengthened by local search. First, all initial individuals would be evaluated by the PSO. Particles that were unable to pass the PSO (lower fitness) would be evaluated by the GA. The two-streamed solutions would be pooled together for local search operation. Mohammadyari et al (2023) hybridized SA-GA in servitude companion type to evaluate the effect of LULC on the distribution of ESs. Crossover and mutation functions of GA were applied at each temperature cycle of the SA to improve the solution quality. The SA initializes random solutions and fitness is evaluated. Selected solutions for the next generation undergo crossover and mutation. The cycle continues until the SA termination criterion is met. Liu, et al (2013) applied the same technique of integrating GA functionality in SA. The advantage of servitude companion hybridization is not just exploiting the advantage of both SA and GA functionalities. The integration of functionalities of one method with another avoids the input-to-output management task that otherwise would occur with simple couplings. The use of nonstandard operators such as the geometric operator in García, et al (2017) and the integration of a Multi-Agent system into the heuristics, say GA, (Zhang, et al., 2010) are other common hybridization strategies to enhance the scalability of the metaheuristic algorithms.
Seppelt and Voinov (2002) acted out of the algorithm environment. They introduced a partially known solution method. Initially, their problem had three objectives (minimum fertilizer use, minimum nutrient outflow, and maximum agricultural output). To facilitate the performance speed of GA, they reduced the objective space to two by first optimizing the minimum fertilizer use objective and then they used the optimal fertilizer use map as an input while optimizing the nutrient outflow and agricultural yield objectives under different land use management schemes. The fertilizer use map underwent a performance check by a Monte Carlo method before its use. It was obvious for the authors to report better convergence for the simulation that inputted the optimal fertilizer use map compared to the problem initialized from scratch. Apart from the classic problem of scalability of global metaheuristic optimization algorithms, the advancement of the research on land use planning context necessitates the hybridization of methods. With an increasing representation of local policies and issues of spatial quality, global optimization becomes insufficient to reflect requirements for explicit local spatial layout requirements. The global and local optimizers coupling are two-step or three-step operations. In the two-step version, global optimizers determine quantitative land use structures and the local optimizers determine the spatial layout of the uses. In the three-step version, one of the local optimizers determines the layout and the other fine-tunes the layout for suitability which is a horizontal process.
Yang et al., 2012 applied ACO, Markov Chain, and CA for modeling a spatiotemporal land use change. Markov and CA were utilized to manage the total amount of land use coverage while the spatial distribution of land use was managed by ACO and CA. The local transition rules for land use change were results of integrating the advantages in ACO and CA whereas the transition matrix that predicts the area of land use change was managed by the Markov chain. The simulation effectively predicted area of the two larger uses and errors occurred for the uses with small areas. Though the authors claim the model’s effectiveness, the spatial matching (quality) turned out to be 73.99%. More importantly, the spatial accuracy of construction land was as low as 58.49%. Area prediction error was at most 18.2% (construction land). However, this does not reflect drawback of the coupling method but may be due to specific setting of the specific problem.
Li et al (2023a) applied multiple methods in view of a comprehensive approach to land use optimization. They coupled multiobjective dynamic planning (MODyP), CLUE-S, and MCR in sequential cooperation coupling format. First, the area requirement of every use was determined based on maximizing ecosystem services by the MODyP. Then logistic regression was applied to identify land use distributions versus relationships among the influencing factors (land use demands, regression results, elasticities of transformation, and the transfer matrix) used as inputs for the CLUE-S that simulates future land use changes and optimize spatial layout of the uses. Finally, the minimal cumulative resistance model was applied to adjust the land structure for suitability zoning.
Li, et al (2023b) criticize existing studies that integrate ecosystem service into land use planning in three aspects; (i) questioning whether spatial evaluation and stakeholders’ survey generate appropriate alternative scheme(s) that shape the effectiveness of the planning decision, (ii) integration of ecosystem service into land use without optimization technology (See Wu, et al., 2018, for instance), and (iii) efficiency limitation of manually generated planning schemes (Hhandayanto, et al., 2017). Li, et al (2023b) claim that government policy restrictions are often hard to be represented in a model easily. In addition, quantification of ecosystem service and land use configuration is hard because the relationship between some ecosystem services and spatial layout is often non-linear. The authors suggested a two-step spatially explicit optimization approach that better embodies ES in land use planning. First, they optimized the land use structure (quantity) by applying MOLP that maximizes ES for different scenarios. In the second step, they determined spatial layout based on suitability objectives that account for biophysical and geographical factors. Their contributions are twofold; horizontal and vertical comparisons of suitability maps and stepwise allocation. After structure is determined, land use allocation would be decided by first looking at spatial units with the highest suitability for each use type. If more units of the highest suitability are available, the units would be compared based on the average value of a respective neighborhood. In the second step, units of the highest suitability for a certain use are assessed for their suitability for other uses too. This current status information is fed to the implementation algorithm at each iteration cycle. Once each use is allocated with its respective highest suitable cells, the information would be fed back into the algorithm for the next iteration for the allocation of the remaining cells based on the second highest suitability. The cycle repeats until allocation of cells exhausts.
Chen, et al (2023) applied LP, MCR, and dynamic-CLUE (DyCLUE) to integrate land use ecological suitability into land use planning in an urban agglomeration scale evaluated for business as usual and ecological restoration scenarios. The MOLP combined the objectives into a single objective for quantitative optimization. The MCR was used to calculate the cumulative resistance that land units overcome during horizontal movement. Resistance factors from sources (ecological and construction) were determined by weighted surface analysis. The MCR returned the ecological suitability zones. The ecological suitability zones are classified by the difference between the two resistance surfaces. The Dy-CLUE explored the optimal spatial layout of the allocations. The Dy-CLUE inputted results of the MOLP model, the ecological suitability zoning map (MCR), and logistic regression coefficients of land use change factors (Traffic and location factors, natural environmental factors, social and economic factors).
Certain optimizers are entirely local-scale applications. The work of Liu, et al (2015) is one. The concern of the authors is how to coordinate local scale competitions within an optimized plan. During a development process, discrete leapfrog construction competes with agricultural or ecological lands. This construction competition may motivate policymaker for early acquisition of the competition zone in the interest of early harmonization. Accordingly, optimization methods need to address the negotiation between the government and agricultural/ecological land use interest holders. The authors applied a dynamic game theory (DyGT) of order-10 to model the negotiation process operationalized by a geometric progression of compensation rate improvement. The government improves compensation offers iteratively. Farmers accept the compensation if current compensation is at least equal to their assessed or perceived income of a certain period. If the compensation offer is below the farmers’ assessed benefit, the deal fails and the government improves the rate. The process continues up to an order n in where either the farmers accept the rate or the government gives up further improving the rate; in either case the deal terminates. If the deal terminates with success, government acquisition shall be effected over the entire competition zone. The authors applied the method to optimize the suitability of land for certain uses and the compactness of the built environment modeled as weighted aggregation. The implementation involved two steps. First, GA was executed for each land use type (farm, forest, garden, development) and an efficient land use map was produced. Then the efficient map would be compared against the existing use map. The difference between the two maps would be the competition zones. In the second stage, the DyGT was applied to determine the final land use allocation. Paritosh et al (2019) applied a similar GA plus GT to solve urban land use problems. In case the competition is among different agricultural uses, Liu, et al (2015) applied planning knowledge to determine the use. The use of the completion zone would be the use type whose area sum is largest in the competition zone.
Zhu et al (2020) applied CLUMondo model to simulate the land use probability for historical trend, government planning, and windbreak and sand fixation scenarios. This simulation method combines land use change with the degree of use change factors and evaluates the effect of land use conversion. The core of the CLUMondo is (i) analysis of land use change driving factors (in their specific work were climate, soil property, topographic, vegetation, socioeconomic, and location) and (ii) consideration of temporal dynamism to the land use planning. The model estimates the priority of a use type for each grid cell by employing the parameters fed to it. The land use type with the highest priority becomes the new allocation.
To summarize, land use optimization method advances emanate from two domains - scalability problems and policies that place special requirements at local scales such as geographic standards of distribution for certain ESs, geomorphological and biophysical quality requirements, transport access, etc. The former problem has been addressed by strategies that enhance the efficiency and effectiveness of global optimizers. Incorporation of knowledge and hybridizing multiple algorithms, one of them has an explorative capacity and another having an exploitative capacity, in different modalities. Simplex-LP methods and partially known solution methods also apply though they appear very rarely. Though there exist situations the hybridization of multiple global optimizers cannot address the conditions of a problem, usually specific restrictions at the local scale, hybrid methods remain more powerful than any standalone single method. To facilitate the understanding of the hybridization approaches and shaping then for further study, we characterize the nature of the hybrid modalities we encounter in the articles we explored based on the degree of integration.
(i) Servitude Companion (SC) - certain functionalities of one global optimizer is mapped into another global optimizer as integral parts.
(ii) Semi-parallel cooperation (SPC) - solutions that are unable to pass one global optimizer is evaluated by another global optimizer and solutions of both streams are pooled together (and may undergo further operation such as by local search).
(iii) Sequential Coupling (SqC) - the output of one (usually the global optimizer) is used as input to the other(s) (usually local optimizers)
(iv) Bonded Integration of Transition Rules (BITR) - rules are drawn from multiple methods and then built into one of the methods as a hosting agent.
Frontiers:
Given hybridizing is contemporarily the state of the art of optimal land use planning methodological approach, many ways to go further can be mentioned. One key frontier is advancing the current relatively weak SPC and SqC to a stronger integration. Designs that make the beneficial part of one method become an integral part of the host algorithm are important so as to avoid input-output flow management among the different methods. In other words, the integration of multiple methods in hybrid methods is often strong where more than one method acts simultaneously rather than one method waiting for outputs of the other. The way Handayanto, et al (2017) applied the PSO-GA coupling is equivalent to testing each method and selecting one. The SA-GA servitude companion Mohammadyari et al (2023) applied and the local transition rule Yang et al (2012) developed from ACO and CA are examples. But such works are less in frequent in application and in diversity.
The effect of parameter setting is unsearched theme in the application of heuristics for the optimization of land use. Each study defines its own global parameters set but follows previous studies’ general information rather than determining own based on experiments. Given numerous parameter and implementation tool combinations, the assessment of the effectiveness of tools remain to be less-objective and more of a general subjective evaluation. The process of refinement of multiobjective decision approaches may be facilitated by developing a standard test spatial problem that is comprehensive enough in terms of parameter coverage and standardized mathematical expressions of each objective parameter (a subset of parameters). Standard test problems are common in Travel Salesman Problem (Cheing and Wahid, 2014; Otman and Jaafar, 2014) and its advanced features such as the Capacitated Vehicle Routing Problem (Kumar and Panneerselevam, 2017), Job Shop Scheduling Problem (Magalhaes-Mendes, 2013), Investment represented by the Knapsack problem (Hhakimi, et al., 2016), and any engineering problems (Alajmi, Wright, 2014).
In addition to the exploration-exploitation capabilities and global and local cooperation that enhance effectiveness of hybrid methods, parameters and temporal dynamics advance its robustness. Yet, studies that examine performance evaluation across different hybrid methods in terms of solution quality, computational cost, and whether the cooperating methods in a certain hybrid are potential research areas that would unleash the full potential of hybrid methods.
While fitness level tells the magnitude of attainment of objectives in the spatial structure a model offers in mechanically artificial indicators, usually it lacks spatial quality evaluations. This is especially true of urban land use optimization. There are situations where neither the knowledge-informed/modified global optimizing algorithms nor resistance to use change objective/constraint is responsive to spatial quality. The highest fitness may be achieved at the cost of spatial quality. This situation calls for the incorporation of objectives or operators that promote the quality of spatial configuration. So far, the only available mechanism is the density-based design (Ligmann-Zielinska et al., 2008) that preconditions allocation of a certain use by the number of existing and newly proposed cells of that use type. However, the method left the task of determining the clustering location to the algorithm’s stochastic decision. In other words, the method is sensitive to the number of target use cells without defining geographic location and turns to be ineffective.
Domain harmony is another issue that needs intervention in urban land use optimization. While it is clear that additive parameters and shape-oriented parameters (compactness, contiguity, number of clusters, size of clusters) are different in nature and the structure of the mathematical expressions are quite different, both objectives are evaluated together without considering the harmonization of mathematical representations. Given no objective is inferior in the Pareto assumption, whether the incompatible mathematical structure has an impact on the overall state is unknown. If so, whether such a mixed domain of objectives problem can be modeled into two sub models where the output of either sub model can be utilized as an input to the other sub model needs attention for a study.
Finally, we note about spatial scale. In the contemporary optimization-based land use planning literature, geographic are the information carriers of the study area (region, watershed, city region, city, district, etc.). Determining appropriate regular cells is a key to balancing the tradeoff scale among objectives. Unstandardized geographic units on the contrary may affect the quality of objective tradeoffs regardless of constraints that might have been met as in Sadeghi, et al (2009). The information carrier unit of Sadeghi, et al (2009) was sub-watersheds of uniform use that were not uniform in size. It resulted in unbalanced tradeoffs among objectives. Irrigation land and rangeland attained only lower bounds, orchard land increased by 93% above its lower bound, and dry farming by 50% above its existing state. The outcome of such allocation imbalance was a high sensitivity of ecosystem services to changing even a single land unit. Reportedly, reduction in benefit showed the highest sensitivity to the reduction of orchard and irrigated farming areas whereas benefit increment was only sensitive to an increase in the orchard area. Similarly, reduction in the rangeland area shows high sensitivity to increased erosion.