## 2 Materials and Methods
### Measuring Spatial Accessibility of the MOH Healthcare Centers Using 2 SFCA Method  
During the past decade, the 2 SFCA method has been used widely to study and analyze the spatial interaction between healthcare providers (supply) and populations (demand) by measuring and assessing spatial accessibility to healthcare. Researchers have preferred to use the 2 SFCA method to evaluate healthcare accessibility due to several factors, the most important of which are (1) the ease and flexibility of data requirements, (2) the possibility of representing the capability of a population to travel over boundaries, (3) the unrestricted utilization of all locations within a catchment threshold with a possibility to deal with overlapping catchments, thus giving more realistic modeling results, as well as, (4) the possibility of using the travel-time threshold to overcome problems of distance impedance within catchment areas. Therefore, the 2 SFCA method was identified as the appropriate method to achieve the purpose of this study, which is to identify and analyze spatial access disparities to the MOH healthcare centers in Jeddah. The 2 SFCA method could catch an area twice according to demand (i.e., population) and supply (i.e., healthcare providers). The 2 SFCA method represents a model of healthcare provider-to-population ratio [36]. It is a method for creating an index that includes a set of combined information to compare among different locations. Measuring spatial accessibility depends on three main factors, which are supply (healthcare providers), demand (population), and travel time between them. Using the 2 SFCA method, a spatial accessibility could be measured as a ratio between demand and supply in two steps with consideration of the impedance measure (i.e., travel time). Practically, such two steps evaluate the availability at the locations of healthcare providers as a ratio to the population who fall within the travel time catchments, and then sum up the ratios resulting from the first step for each population location [35]. The 2 SFCA method uses the dichotomous distance decay function to create a map of spatial accessibility scores to be classified as accessible-inaccessible by considering the travel time catchment areas. Practically, this function assigns accessible value = 1 within the travel time catchments and inaccessible value = 0 outside of catchments. In other words, equal weights of 1 are given to all population falling within the catchments in both steps (i.e., full accessibility score); thus, they have accessibility to healthcare services. In contrast, equal weights of 0 are given to all population falling outside the catchments (i.e., accessibility score is zero); thus, they have no accessibility to healthcare services, and this indicates that the population of such areas should travel beyond the catchment threshold to access healthcare service [32; 34; 35]. The results are indexed scores of spatial accessibility that reflect the level of accessibility for population related to each demand location (i.e., district centroid). A spatial accessibility to healthcare services is evaluated according to a scale that includes a lowest score and the highest possible score. The lowest score is zero, which means no accessibility to healthcare, while, the higher the accessibility score, the greater the access to healthcare. Thus, if the supply is greater than demand, it is expected that the score of accessibility will be greater for the population residing close to healthcare services. On the other hand, the score of accessibility will be low if the demand is highly greater than the supply, even if the distance between the demand and supply is small [35]. Nevertheless, the 2 SFCA method could be represented by the following two steps [32]:Step 1.