Current location:

Iso-route

Applicability:

Cadcorp SIS Map Modeller
Cadcorp SIS Map Editor
Cadcorp SIS ActiveX Modeller

Ribbon Group:

Analysis-Routing

Conditions for use:

Item Class:
Minimum number selected: 1
Minimum item status: Editable

Associated commands:

Point-to-point

Description:

Iso-route constructs an iso-route (traced network) from a point.

The iso-route is traced over existing graphics which shows the distance you could travel if you were leaving from a given point and your journey was subject to given conditions.

SIS creates the iso-route as a MultiLineString item, which covers all the places that can be reached. As it overlays existing data, it is best created on a different overlay from the original data, so that you can view it easily.

On selecting this command the Iso-route dialog will be displayed:

Shortest

Select this option to show all locations that can be reached via a route which is shorter than the distance entered in the Limiting value field of this dialog.

Expression

Select this option to use an expression to calculate the iso-route. For example, an expression may be used to take into account the speed limits on the roads in order to calculate an iso-chrone based on time rather than distance.

Limiting value

This field will use the current linear units (set by CRS [Home-Map], Units tab).

Example

To construct an iso-route which covers all places on a street map which are within 1000m of a hospital. Alternatively you could carry out drive-time analysis and find out where you could reach in a given time when starting from a given point and driving at a given speed (which would be useful at a Fire Station).

Make a suitable overlay the current overlay.
Select Iso-route
In the Iso-route dialog choose whether the route taken should be the shortest, or whether it should be based on an expression (e.g. distance divided by speed, to give time).

If you ask SIS to find the shortest route, the _length# property of the items is used.

You could create an expression to enable the “cost” of each link to be used, or if the expression were:

_length#/SpeedLimit&

then the time for each link would be calculated.

Note: the attribute SpeedLimit& must exist for each link.

Enter a limiting value. This gives the furthest point to which the iso-route is constructed in any direction from the starting point.

If you chose to base the route on the shortest distance, you need to select that option and enter the limiting value in the Iso-route dialog:

This example shows an iso-route that will be constructed 1000m (assuming current linear units are set to metres) in all directions from the start point.

If you chose a time-based expression (e.g. distance divided by speed), this should be the number of seconds to travel, this will create an iso-chrone.

Click a position to start the iso-route from.

The iso-route is created. If it was created on a separate overlay from the original data, you will be able to view it separately and use it to create a Buffer.

Starting from the X point in the following road network could result in the iso-route shown on the right.

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