1. Introduction
Urban vitality is a central topic in 21st-century urban agendas. According to the United Nations (UN), an estimated 60% of the world’s population occupied urban areas by 2021, while South American numbers increased to 82% of the total [
1]. This urban expansion presents considerable challenges regarding the sustainability of the planet. In this regard, the UN suggested in the year 2016 seventeen Sustainable Development Goals (SDG) to guarantee the human growth viability [
2]. The eleventh goal, Sustainable Cities and Communities, highlights the significance of conceiving good places to live, which must include a transversal answer to environmental, economic, and social requirements. Descending this concept to a small urban scale, the perception of a successful neighborhood is related to the idea of self-sufficiency and proximity, having the possibility of close access to food supply (shops, supermarkets), health (hospitals, recreation areas), education (kindergartens, schools, universities), and housing, placing the commodity and quality of life of the inhabitants in the center of the urban discussion [
3].
One of the pioneers in the study of urban vitality was the American Canadian city theorist Jane Jacobs (1916-2006). She wrote a highly controversial book in 1961, “The Death and Life of Great American Cities”, which remains valid more than sixty years later. In the first chapter, Jacobs pointed out the importance of people’s concentration in the achievement of urban vitality. According to this, she presented sidewalks as one of the main elements in the nature of cities. She coined the expression “eyes on the street”, referring that having people walking around and looking through windows would guarantee street safety, among others [
4]. In the second chapter, Jacobs analyzed diversity, relating it primarily to economic and morphologic factors, concluding that the need for primary mixed uses, the need for small blocks, the need for aged buildings, and the need for concentration of people were substantial dimensions to provide urban vitality. In the third and fourth chapters, she highlighted the importance of reducing border vacuums, referring to big urban areas with massive single uses, and having good accessibility as additional complements to motivate people to walk on the streets [
4].
Since the 1970s, a significant number of authors have reviewed and interpreted Jacobs’s approach defining several indexes, composed of different dimensions and, at the same time, structured by a sum of indicators: the index of total diversity[
5], the primary diversity index [
6], the Jacobs’s diversity index [
7], the compact city index [
8], the Simpson diversity index [
9], the Shannon’s index [
10], the walkability index[
11], the entropy index [
12,
13], the gravity index [
14], the JANE index [
15,
16,
17,
18], the urban vibrancy index [
19], the Morphoindex [
20], the urban form index [
21], the urban comprehensive vitality index [
22], the urban vitality index [
23], and Moran’s index of urban vibrancy [
24]. Additionally, the total number of publications regarding urban vitality increased by 527% from 2008 to 2018 [
25].
Most studies of urban vitality have been developed in Asia, more specifically in China, Shenzhen [
26,
27,
28], Hong Kong [
29], Shanghai [
27,
30,
31], Tianjin [
27,
32], Chengdu [
27,
33,
34], Wuhan [
27] and Qingdao [
18,
27]; in South Korea, Seoul [
7,
35,
36,
37]; in Singapore, Singapore [
20]; in Vietnam, Ho Chi Minh [
38], and in Turkey, Kayseri [
39]. To a lesser extent, similar investigations have been conducted in North America, more precisely in the United States, with special attention in Seattle and Washington [
11], followed by Manhattan [
14,
40], Portland, Brisbane, Indianapolis, and Chicago [
14]. In Australia, Melbourne, and Adelaide [
14] have been studied. In Europe, research has taken principally place in England, London [
41]; in the Netherlands [
42,
43]; in Italy, Bologna, Florence, Milan, Palermo, Rome, and Turin [
44,
45]; and in Spain, Barcelona [
15,
17]. Finally, in South America, only Santiago, in Chile, has been analyzed [
16].
The definition of a clear geographic scale is essential to comprehend urban vitality [
35,
46]. Investigations have predominantly focus on the metropolitan scale [
7,
28,
36,
38,
47]. However, some studies pay attention to the district and neighborhood scale. According to this, [
17] compares the thirteen neighborhoods that conform the district of Nou Barris in Barcelona, but without descending to the block scale. [
48,
49] approach the block scale but only examine the accessibility dimension. [
18] proposes a decrease in scale, but not exactly defining the conditions per block. The fact of not accentuating the importance of the block scale could lead to a misunderstanding of the closest environment, the belonging space, and the essence of urban vitality [
50].
The scale of the study area is directly related to the representation system. Two main spatial representations are used to map urban vitality: the raster-based and the vectorial-based. In most cases, the first one uses a regular raster of squares, which adopts a quantitative gradient of pixel divisions, symbolizing the ponderation of the chosen categories. Moreover, the size of the study area usually determines the pixel area. The smallest ones, around 50x50m, include districts or neighborhoods of study [
17,
39], while the large ones, from 100x100m up to 250x250m, usually provide the analysis of the whole area of a city [
15,
16,
51,
52] or the comparison of various metropolis [
20,
27,
53]. The second representation method uses the administrative boundary of districts or neighborhoods, which commonly coincides with the street layout [
11,
38,
54,
55,
56]. Additionally, another interesting way of illustrating urban vitality is mapping continuous lines on the street layout with different gradient colors, leaving the blocks empty [
34], using alternative diagrams with different sized and colored circles and linear diagrams based on x and y coordinates [
31] and 3D space-time cubes [
28].
The review of studies on urban vitality in the last ten years allows us to identify two major research gaps that structure the present research: i) there is a lack of studies on urban vitality at block scale in the Andean region, ii) there is no evidence of the application and comparison of different indexes in a single case study. Regarding the first gap, only one study uses GIS quantification to measure urban vitality, more specifically in Santiago, Chile [
16]. Nevertheless, there is potential practice-oriented research since several initiatives in Argentina and Ecuador examined urban morphology to inform sustainable principles at a neighborhood level, although not directly applying urban vitality indexes [
49]. On this subject, it is worth mentioning Salvador Rueda, who carried out several projects in agreement with the Municipality of Quito, in which he developed the Superblocks Study at the Historic Center of the city between 2013 and 2015, promoting private traffic reduction and active mobility [
57]. The Llactalab laboratory in Cuenca, Ecuador, developed a GIS tool on urban morphology and sustainability [
58]. Additionally, studies do not usually illustrate urban vitality with a morphological characterization and representation of blocks. Nevertheless, this is probably the most appropriate scale of analysis considering the daily component of the movements of the inhabitants within the area. Concerning the second gap, there are no publications, which illustrate the application of more than one index of urban vitality in the same study area, avoiding the possibility of contrasting results.
According to these gaps, the present work aims to provide a comparative approach, by the application of different indexes at a block scale in the same study area, La Mariscal neighborhood, in Quito, Ecuador, replicable in other Andean cities. Objectives are aligned to contrast different dimensions, indicators, and representation proposals. Research questions are: Which criteria can orient the selection of dimensions and indicators for measuring urban vitality? Which representation system is more precise for measuring urban vitality at a block scale? In this sense, we focus on morphological features derived from Jane Jacobs's approach. The remainder of this paper is organized as follows:
Section 2 describes Materials and Methods;
Section 3 provides the Results,
Section 4 discusses the paper's findings, and
Section 5 states the conclusion.
4. Discussion
The present study's results contribute to discussing the two research questions: Which criteria can orient the selection of dimensions and indicators for measuring urban vitality? Which representation system is more precise for measuring urban vitality at a block scale? Moreover, future lines of research are suggested.
Regarding morphological dimensions, it is essential to define which are the most relevant in each particular study area in order to reshape Jacobs’s approach. To this extent, the density dimension highlights notable differences depending on the context. In several contemporary Chinese neighborhoods, it is associated with high-rise buildings [
28,
29,
64], while in European areas conceived as city extensions in the second half of the 19
th century, like the Eixample of Barcelona, it refers to urban compacity, represented by approximately eight-story buildings inserted into compact blocks [
15]. Furthermore, Chinese cities such as Shenzhen, Nanjing, and Chengdu present an indissoluble connection with the land use mixture dimension [
26,
34,
65]. Moreover, in Turkey, more particularly in Kayseri, special attention is put on the creation of a need for small buildings' dimension [
39]. In addition, the contact opportunity and aged buildings dimensions are notably remarkable in cities where historical layouts are predominant [
15,
17]. Likewise, even though the accessibility dimension was secondary for Jane Jacobs’s approach in the 1960s [
4], it is crucial for urban vitality calculations in the present, not only because of the importance of public transport stations, but also for the relevance of integrating vulnerable collectives such as children, the elderly, or people with disabilities in the composition of urban areas [
66,
67,
68]. Besides, the border vacuums dimension needs to be extremely precisely defined, for instance, the inclusion or exclusion of big parks, depending on their role in the study area. This difficulty in defining the specific characteristics of border vacuums is probably the reason why it is not included in several indexes of urban vitality [
1,
2,
3]. In the specific case of La Mariscal, the land use mixture, contact opportunity, and accessibility dimensions play a very significant role. The first one as a consequence of the remarkable number of restaurants, bars, discotheques, political institutions such as international embassies and consulates, and public and private schools and universities located in the area. The second one due to the historical layout heterogeneity of the neighborhood. The third one because of the significant number of residents, who use public transport to move inside Quito, more than 70% of the total [
69,
70].
Regarding the indicators’ selection for each dimension, two main criteria are recommended: context and scale. It is essential to add context-related indicators to reinforce the connection to the study area and to incorporate more building-scale morphological indicators to gain accuracy. Regarding the first, the inclusion of four new context-related indicators in the case of the Andean region would substantially improve the urban vitality measurement. First, an informal small-scale commerce indicator, very common and a determinant of urban vitality. Second, a quality of sidewalks indicator, meaning having no barriers to generate continuous walking with a wheelchair or similar, as a result of the insufficient level of quality of a significant part of the streets in the region [
48,
71]. Third, a slope indicator due to the complex orography in most of the cities of the region. And finally, a good-conditioned street furniture indicator, including banks and big trees to protect from the high UV factor in the countries close to the Ecuadorean line, either in parks or streets. Besides adding new indicators, a deep understanding of the context would facilitate reconsidering the street width indicator, which illustrates a controversial topic connected to the culture of the place. For instance, in Mediterranean cities, there is a context-based concern that relates pedestrian streets (usually narrow) with walkability and, consequently, urban vitality [
3,
48]. On the contrary, in the Andean context, people tend to concentrate more on wide streets where public transport stations are located, due to the unusual presence of pedestrian streets [
72]. According to building scale new morphological indicators, façade length and door encounter rate [
40], and building entrance density [
35], would reinforce the block characterization’s relevance in relation to what happens on the ground floor, which highly determines urban vitality worldwide, including the Andean context. Besides context and scale criteria, it becomes also fundamental to evaluate on how to calculate the indicators. For instance, in several studies, the distance from border vacuums indicator measures the distance to these areas using the proportional color gradient representation [
15,
16,
17]. However, we think that it should be reinterpreted, simplifying its calculation to presence or absence, assuming that its influence will be no longer than a maximum of three blocks. Moreover, the POI designation, which concerns the calculation of several indicators, should be weighted according to the specific role of each building in the study area [
26], usually related to the use and size. For example, in the case of the La Mariscal, restaurants, bars, and discotheques are part of the area’s main attractions, as well as political institutions, such as international embassies and consulates. Likewise, there is a metropolitan pediatric hospital, called Baca Ortiz, occupying the whole block, which promotes more urban vitality than a small restaurant, due to its size and 24/7 schedule.
Ultimately, the question of the most precise representation system for measuring urban vitality has been a subject of great interest among urban researchers. On one hand, the use of raster calculations in this context has revealed a lack of correlation with urban morphology, particularly at the street layout level [
20,
53,
73,
74,
75,
76]. However, the use of a small-scale unit of measurement, such as a 50 x 50-meter raster cell, has shown promise in identifying hot and cold spots. On the other hand, the use of a block (polygon) representation as a unit for calculation has been shown to clearly connect the specific urban layout to urban vitality, albeit at the expense of excluding some street and plot characterization [
18,
19,
33,
45,
65,
77]. In light of these findings, it is noteworthy to consider a combined approach that leverages both rastering and polygonal results, for instance by descending to the plot analysis, to comprehensively understand urban dynamics at a block scale. Such criteria would allow for a more nuanced understanding of the relationship between urban morphology and vitality, and enable the identification of specific urban features and patterns that drive urban vitality at the block scale.
Limitations of the present article and future lines of research
Two types of limitations are worth mentioning for this study: methodological and conceptual. Regarding the first one, official open data sources are almost inexistent in Ecuador. In the specific case of Quito, official data present access problems and certain incoherence, due to the update limitation by the local government agencies. On this subject, there is no official data regarding de Building Use Mix Indicator (BUMI) and the Residential Non-Residential Balance indicator (RNR). The data used to calculate these indicators was manually raised in 2022. Furthermore, the last national census was developed in 2010, generating some possible inconsistencies concerning the permanent population of the study area.
Regarding conceptual limitations, although the application of the three selected indexes has offered a rich array of dimensions and corresponding indicators, in representative current studies on urban vitality focused on morphological parameters a lack of inclusion of the time dimension has been identified. In this regard, future approaches should include time-sensitive indicators. For instance, land use influence on urban vitality changes during day or night hours (f.i. discotheques at night), and on week or weekend days (f.i. schools). Time-based indexes of urban vitality would contribute to a more detailed understanding of morphological parameters that determine people’s activities [
19,
52,
75]. This could also promote the assimilation of the variability concept, which refers to a dynamic attribute regarding the flexible quantity of people present in the same area at different times of the day [
41,
78]. Moreover, the inclusion of time in measuring urban vitality may also lead to a significant relationship between people’s concentration and street security [
29,
79].
Finally, the morphological approach used for this study could be enriched with complementary data on people’s activities (f.i. mobile phone big data on people’s daily mobility) and sociodemographic data [
76,
80,
81].
Author Contributions
Conceptualization, Nuria Vidal Domper, Gonzalo Hoyos- Bucheli and Marta Benages Albert; methodology, Nuria Vidal Domper, Gonzalo Hoyos- Bucheli and Marta Benages Albert; software, Nuria Vidal Domper; validation, Nuria Vidal Domper, Gonzalo Hoyos-Bucheli, and Marta Benages Albert; formal analysis, Nuria Vidal Domper, Gonzalo Hoyos-Bucheli, and Marta Benages Albert; investigation, Nuria Vidal Domper, Gonzalo Hoyos-Bucheli, and Marta Benages Albert; resources, Nuria Vidal Domper, Gonzalo Hoyos-Bucheli, and Marta Benages Albert; data curation, Nuria Vidal Domper; writing—original draft preparation, Nuria Vidal Domper; writing—review and editing, Nuria Vidal Domper, Gonzalo Hoyos-Bucheli and Marta Benages Albert; visualization, Nuria Vidal Domper; supervision, Gonzalo Hoyos-Bucheli, and Marta Benages Albert; project administration, Nuria Vidal Domper, and GonzaloHoyos-Bucheli; funding acquisition, Nuria Vidal Domper, and Gonzalo Hoyos-Bucheli. All authors have read and agreed to the published version of the manuscript.