Reachibility Analyses
You want to draw the catchment area for a new shop. From where can pedestrians get to the place within 10 minutes? What's the area for a 30-minute drive?
A reachability analysis answers these questions by looking at OpenStreeMap's road network. The result comes in the form of a "spider web like" partial road network, containing all the bits that are no more than the predefined number of minutes away from your starting point.
In addition to the partial road network, the algorithm also generates two sets of zone polygons - one "area" shape with the full catchment area in a couple of steppings (e.g. the innermost polygon covers 0-15 minutes, the next larger one 0-30 minutes, etc.), and one "ring" shape that covers only the respective area (0-15, then 15-30, etc.).
Creating a new analysis
To create a new analysis, click on the new analysis link in the navigation bar on the top right.
You can configure the following properties:
Origin
Place the marker on the map to the point of origin for the analysis. Zoom to the general area, then click on the map to place a marker. You can move the marker afterwards for preciser placement.
Mode of travel
Select whether you want to analyse for pedestrians or for automobile traffic.
If you go for pedestrians, then additional streets and paths will be considered that are are unavailable for motorized traffic. Also, a standard walking speed will be assumed for all street types.
If you select all streets then all streets open for motorized traffic will be used in the analysis. The system will assume average driving speeds for the different street types.
Finally, choose long distance roads if you want a large-area analysis; small residential and service roads will be omitted from the analysis, yielding a coarser but less data intensive result set that might be easier to post-process than the fine-grained result you get from the all streets setting.
Distance in minutes
Set the distance for which you want to run the analysis. Larger values will yield larger result data sets, including more of the street network.
Zone smoothing
The first result of the analysis is a street network. From this, we will compute a couple of zone polygons to approximate the area that can be reached within a certain time. The smoothing setting controls how close the result will be to the exact road network. Coarser smoothing usually yields more visually appealing results.
Zone stepping in minutes
While the core algorithm works with a 5-minute stepping, computing one polygon for each 5-minute zone would lead to strange looking results and degraded polygons. We will usually group results into 15 or 30 minute steppings for better results.
Download the result
After you have started a new analysis, you will be sent to the detail page for it. Initially, your analysis will show as "new" or "running", and when it has been completed after a few minutes, a download link will be shown. The download is for a zip file with three shape files - a linear file for the computed road network, and two polygon files (one areas, one rings) for the zones.
The Jobs link in the navigation bar gets you to an overview page of all the jobs that you have computed. From here, click on a job to access its detail page where you can reveiew the parameters and request a download.