In addition to the expansion to global coverage and a much expanded road classification, Freeway now supports multiple levels of resolution. The original model included only two resolution levels – normal and detailed – which were at the 500’ and 2500’ grid levels. Our new model includes four resolutions to cover a broader range of applications –
- Fine (250’)
- Normal (500’)
- Moderate (1000’)
- Coarse (2500’)
As in previous versions, setting the mode to ‘automatic’ results in a system chosen resolution based on the input drive time in order to minimize run times for large areas, as processing times increase with radius squared rather than in a linear fashion.
With Freeway Global, the normal resolution remains the best choice for typical drive times (5-15 minutes). The fine resolution is well suited to small drive time polygons in densely populated areas for either automobile, walking, or cycling applications. The moderate and coarse resolutions are used for large drive times, or for inter-city travel.
To show the differences between polygons generated at various levels of resolution, we created a 15-minute drive time in downtown New Orleans using three resolutions (fine, shaded in light purple), normal (outlined in gray), and moderate (outlined in dotted red). While the differences are minor, they can result in differences in the reported demographics based on the block centroid coordinate locations.
The second map is zoomed in close to one part of the polygon – and here the differences in resolution of the underlying grid can be clearly seen.
How do you choose what level of detail to use? For most purposes, the automatic mode will be the best choice since the resulting polygons will generally be appropriate for the map display scale. Extremely detailed but large polygons may in fact cause a map viewer to not be able to see the forest for the trees – as eyes are easily drawn away from the general shape and extent of the drive time to focus on the fine details at the edge. We recommend setting a resolution only in cases where multiple trade areas are being generated for the same site, as this will ensure consistency in the output.