Isochrones

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This menu item covers a wide selection of actual isochrone calculations and then the service area method, many of them sharing the same list of input parameters.

 

Methods:

 

Linked-based

Simple

Voronoi

Alpha shapes

Service area

 

Input:

 

A point based table in either TAB or SHP format.

For most of the methods it is also required to select an ID field.

 

Steps can be either minutes or km, according to choosing either fastest or shortest route. This applies to all methods, except the service area.

 

"Add nodes" determines how many artificial nodes are created along the link, between the real nodes of a link.

For instance a 2 km link with addnodes = 0.5 would add nodes at 0.5, 1.0 and 1.5 km.

Low values may add a huge number of nodes and slow down calculations a lot and require more RAM.

Normally don't go below 0.1 km or set it to 0 for no additional nodes at all (large networks).

 

"Angle" is used for simple isochrones. Either set it to 0 or some low value such as 3.

 

Smoothing can be enabled, but may give degenerate results in some situations.

 

 

Table of methods and possible parameters:

 


Steps

Keep Islands

Keep Holes

Doughnut

Smoothing

Add Nodes

Angle

Link-based

X

 

 

 

 

 

 

Simple

X

 

 

X

X

 

X

Voronoi

X

X

X

X

X

X

 

Alpha shape

X

X

 

 

 

X

 

Service area

 

X

X

 

 

X

 

 

 

Methods marked with a (*) generate one table as output for each record in the input table. The output tables are all named with _ and the content of the ID Field.

 

The 2 methods marked with a (+) use nodes as starting point in the calculations, while the rest all use the more accurate dynamic segmentation.

 

 

Note: The 3rd method above was removed in build 2.2.0.5.