View source for Travel Distance Overlay

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[[File:Travel_Distance_Overlay1.jpg|thumb|300px|Travel Distance overlay for 500m travel distance to a school (blue arrow), over roads with pedestrian traffic (sidewalks)]]
The Travel Distance [[Overlay]] is a [[grid overlay]] which shows the distance that can be traveled from a certain starting point (routing [[Area|area]]). The traffic is split between motorized and pedestrian traffic, based on the road type (roads vs sidewalks). 

The overlay also uses an additional fill distance, which allows the result to expand to the area around the accessible roadways, to include accessible surrounding constructions. This allows users to query constructions that are within acceptable distance of cells which are within the travel distance.

The calculation model behind the overlay is based on the same algorithm as used in the [[Watershed Overlay]]. The travel distance will therefore not be the exact travel distance, but the 8-direction [https://en.wikipedia.org/wiki/Chebyshev_distance Chebyshev distance].

===Example===
The travel distance overlay can be used to visualize the travel distance from certain areas of interest (schools, shops, sports centers, etc), based on the roads project area. If we take a school as example, we can visualize which houses (and other buildings), within a range of 20m to a connecting sidewalk, are within a walking distance of 500m from the school of the example.

===Keys===
[[Travel_features_(Travel_Distance_Overlay)|Travel features]]:
* [[Destination_area_(Travel_Distance_Overlay)|DESTINATION_AREA]]
* [[Blocked_(Travel_Distance_Overlay)|BLOCKED]]

===Attributes===
* [[Model attributes (Travel Distance Overlay)|Model attributes]]

===Grid Prequels===
It is also possible to provide certain input data as more detailed grid. The following data can be provided as prequel [[Grid Overlay|Grid Overlays]]:
* TRAVERSABLE: Provides an alternative for the traversable grid locations. Overrides the default, which are traversable roads which allow car or pedestrian traffic.
* BLOCKING: Provides an alternative for the non-traversable grid locations. Overrides the blocking features configured using [Blocked_(Travel_Distance_Overlay)|[BLOCKED]].

===Result Types===
{{result types|suppresscategory=true|allowselflinks=true|
  {{:Distance result type (Travel Distance Overlay)}}
  {{:Base types result type (Travel Distance Overlay)}}
}}

==How-to's==
* [[How to add the Travel Distance Overlay]]
* [[How to create a Destination area]]
* [[Area#Adding, duplicating and removing areas|Adding, duplicating and removing areas]]
* [[How to add and remove an Overlay]]
* [[How to edit an overlay legend|Edit an overlay legend]]

==Notes==
* A likely improvement will be the support of diagonal travel distance, also known as ''octile distance''. Here the diagonal distance between two cells is <math>\sqrt{2}</math> times the cell size, instead of the same distance in all eight directions.
* This method does not take into account driving lane and one-direction limitations.

{{Overlay nav}}
{{TravelDistanceOverlay travel features nav}}