In GIS, ‘proximity’ to a location is measured in straight lines (euclidean distance or distance ‘as the crow flies’). Using a simple buffer analysis, common proximity questions like - suppliers located within 25 miles of a construction site or stores within 5 miles of a postcode – can be answered. An alternative approach is to derive the catchment (service areas) reachable by different transport modes (walk / driving a car / public transport) using road network models. Compared to the buffer analysis, this approach is more complex and requires up-to-date transport network data and software extensions to implement in desktop GIS. Although subscription services are available from various vendors, accessing this across different GIS platforms can be challenging.
As most of the modern day commuting from place A to B involves multiple modes of transport, this can add an additional layer of complexity in catchment mapping. When choosing a location in terms of access, it is more often sensible to use the time it takes to reach by common transport modes rather than the distance. It is all the more powerful when public transport timetables are also integrated within the travel time estimation. Traveltime Platform offers an API which allows travel time catchment calculation using a combination of travel modes for the entire UK.
Our prototype application uses the Traveltime Platform API to generate the travel catchments which are saved as geojson in a PostgreSQL database and are then converted to PostGIS geometry objects using ST_Transform, ST_SetDRID and ST_GeomFromGeoJSON constructors. Using this approach, travel catchments can be created on the fly which will be available for spatial analysis in the desktop as well as online environments.