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ŠUMARSKI LIST 9-10/2018 str. 39     <-- 39 -->        PDF

In accordance with the defined objectives, the following hypotheses were posed:
a) the settlement of Zadar is a heterogeneous unit because there are significant differences in UGS accessibility and quantity among statistical circles;
b) large areas of UGS within the settlement do not necessarily generate equal satisfaction regarding their accessibility;
c) the perception of citizens and the UGS accessibility indicator coincide.
Numerous empirical studies (Jim and Chen, 2006; Qureshi et al., 2010; Irvine et al., 2013) have indicated that UGS have specific functions at different levels of urban life. Urban forests can play a significant role in urban areas in the context of weekend recreation, while smaller parks located in the city centre have a stronger connection with local daily activities and socializing (Chiesura, 2004; Oh and Jeong, 2007). Since UGS accessibility aims to reflect community needs, it is important to consider different functional levels. The functional level means that green spaces of smaller (residential green) and larger areas (urban forest) cannot replace each other because residents perceive them in different ways and use them for different types of activities (Van Herzele and Wiedemann, 2003).
Accessibility is defined as “relative ease” of approach to specific attractive locations from certain places (Luo and Wang, 2003; Mak et al., 2017) and how visible the site is to the public. Accessibility usually refers to the non-linear distance travelled in the specific time unit without the use of means of transportation, from the user’s location to his closest green space (So, 2016). Although the definition of accessibility is relatively simple, its implementation can be quite challenging, due to the characteristics of the city’s transport network (Comber et al., 2008). In this paper, UGS accessibility is expressed as a percentage that represent the share of the population within specific statistical circle which has accessible specifically UGS functional level.
The work methodology was based on the integration of general scientific and specific geomatic methods, which included a multispectral satellite image analysis using the supervised classification method, vectorization of high-resolution digital orthophoto (DOP) images, GIS spatial analysis, and statistical and cartographic visualization methods. The research process was designed and implemented in four stages.
The first phase of the research was related to analysis of the literature about UGS with the aim of determining standards based on which the accessibility indicator would be created. Seven objective measures for the evaluation of statistical circles were defined. These included: 1) UGS-a (m²) per capita and 2-7) accessibility (%) according to UGS functional levels.
In the second phase of research the first full spatially oriented UGS database for the settlement of Zadar was created following the methodology of Urban Green Belts Project (UGB) WPT 1 Activity 1.1 (Zadar Nova, 2016). The database was created using multispectral images (USGS, 2017) and the high resolution DOP images (DGU 2017). Supervised classification of LANDSAT 8 multispectral images, with a spatial resolution of 25 m, was performed and UGS were extracted from the settlement of Zadar. The derived model of land cover was modified and adjusted using data collected through the hand vectorization method of high-resolution DOP (pixel size = 0.5 m). The combination of different data sets delivers a higher value of output data, which provides more potential for analysis and a better interpretation of the model.
In the third phase, the objective measures required for generating the UGS accessibility indicator were derived from the created database. An accessibility analysis according to the Accessible Natural Greenspace Standard (ANGst) and UGS functionality level was performed using the non-linear distance and travel time variables. In this case, walking time (min.) and regular distance (m) were used as a cost attribute. The ANG standard was defined to evaluate access to UGS and identify statistical circles which lacked green space. According to this standard, and regardless of where they live, everyone should have access to UGS of at least 2 hectares, and not further than 300 metres or 5 minutes walking distance from their home (English Nature, 2003). Analysis was performed using the walking distance “cost” (min.) from geoobjects, which represented the urban infrastructure, to UGS access points (Comber et al., 2008; Gupta et al., 2016). UGS access points were determined by overlapping the traffic nodes and UGS layer with DOP. The functional levels of UGS were determined according to the size of their area (Van Herzele and Wiedemann, 2003) and their accessibility was determined based on the parameters of walking time following a systematic process:
a) From the UGS database, classes representing residential green (up to 1 ha), neighbourhood green (1-5 ha), quarter green (5-10 ha), district green (10-60 ha), city green (60-200 ha) and urban forest (>200 ha), were selected. Using the Network Analyst extension accessibility zones were produced around previously created UGS functional levels.