## 2 Materials and Methods
### Network Analysis  
An approach of network analysis is an appropriate approach to deal with routing and transport issues by providing accurate and quick solutions [55]. Several inquiries related to linear networks can be answered by network analysis, especially with advances in the GIS technology recently. This type of analysis requires an availability of network data to find distance between two points within the network. The network data are represented in linear features, such as streets, roads, rivers, etc. A set of applications could be created using the network analysis, the most common of which are: (1) finding the best route or the closest facility by travel time or distance, (2) calculating service areas to determine areas within a specific travel threshold, (3) creating the OD cost matrix to find the cost to access the closest destinations from each origin, and (4) identifying the location of the new facility that provides the best response times for the community, etc. [50,56,57].  
The ArcGIS Network Analyst Extension provides the network-based analysis that can spatially solve various routing problems. This analysis could be performed using many spatial tools, such as new route, new closest facility, new service area, new OD cost matrix, and new location-allocation analysis [50,55]. Users use the Network Analyst to solve many problems and inquiries of their network requirements. In other words, the Network Analyst provides several features that enable users to find the quickest or shortest route, plan routes, allocate new facilities, estimate drive-time service area, and so on. The network could also include some cost values (e.g., slope, distance, time, or other flow attributes) [50]. Furthermore, users could utilize the Network Analyst to dynamically produce a network based on realistic conditions, such as speed limits of roads, turn restrictions, and traffic characteristics. To run tools of Network Analyst Extension, the network dataset under ArcCatalog module should firstly be created based on the road network that includes the travel time value for each road (line segment) within the study area [55].  
To perform the network analysis task, all data, such as population districts' boundaries and healthcare centers, should be consistent with the road network dataset, as well as in a format that a user could spatially map and analyze (e.g., population districts' boundaries that are presented as polygons should be converted to point shapefile) [34]. The point shapefile can be produced by using the \"Feature to Point\" function within the ArcGIS Software. In other words, this function creates centroids that are used to represent the districts of Jeddah. The use of this feature allows snapping of centroids along the road lines at the closest point to the network for the analysis. By this process, network distance measurements from the facility location can be determined. The district centroid representsthe center of demand point for a population that a district polygon includes. Such a demand point is then used, along with the facility location point, to calculate the network distance that identifies which populations are within the drive-time catchment area [35]. Overall, using this feature is useful, especially given that some districts of Jeddah include limited main and secondary roads. However, the tool of \"Origin-Destination (OD) Cost Matrix\", which falls under the ArcGIS Network Analyst Extension, is used in this study to execute the 2 SFCA method. The OD matrix is used as a source for calculating provider-to-population ratios, and scores of spatial accessibility for population districts.