The research team will investigate how accessibility of city blocks is quantified through the transport systems utilizing real traffic flow data from the Los Angeles Metropolitan Area. Accessibility is a complex function of origin locations, destination locations, the underlying transportation network, the dynamic weights on the edges of the networks representing travel times during different times of the day, etc. To understand accessibility, a proper evaluation of accessibility is essential. One major way to evaluate the accessibility of public facilities such as hospitals is reachability analysis which determines whether certain city blocks can be reached from at least one of these facilities within a certain time span. An isochrone is generally defined as a curve drawn on a map connecting points at which moving objects (e.g., cars) arrive at the same time if they leave from the same origin, and it is one of the most efficient tools used in addressing the reachability analysis problem. The investigators will define the isochrone and reverse isochrone problems, describe their approach to solving them, and provide a functional system that is capable of visualizing the reachability in various ways.