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Property Counting

InfoWorks polygons have three data fields used to provide information about population within the polygon.

The data fields are:
  • Number of Properties - this value can be entered manually, or calculated using one of the methods described here
  • Occupancy Rate - a multiplier for the Number of Properties value to give Population.
  • Population - this field is always read-only. It is calculated from Number of Properties multiplied by Occupancy Rate.
You can generate property count and population data for your polygons in two different ways:
  • from GIS data by importing a layer or table containing address point or population data. The method depends on which GIS component you are using in InfoWorks.
  • from the existing demand data in the network. The rest of this topic concentrates on describing this method.

Calculating from GIS

The GIS file must contain Point data. You may already have population or property data in the correct format, or you can create a file based on data from several sources:
  • Local Authority population census data
  • Building seeds (points representing the centres of buildings) from a DXF file

InfoWorks calculates a value for the Number of Properties field from the GIS data supplied.

The Population value for a polygon is calculated from Number of Properties multiplied by Occupancy Rate. So you can use a variety of people based or building based data, and get a sensible value for Population by setting a reasonable Occupancy Rate factor.

To calculate property counts using data from GIS

  1. Open the network containing the polygons you want to update. You may need to change the flags on the Number of Properties field for your polygons. The process only updates the field if the #G flag is set. To change flags:
    • Click the button or choose Window Grid windows New polygons window. Choose the Polygons tab. This displays the Polygons Grid View of the Polygons Grid.
    • The Number of Properties field must have the #G (geographical) flag before a polygon will be updated by this process. If you do not want a polygon to be updated, set the flag to something other than #G.
    • Make the GeoPlan Window for the network the Current Active Window.
  2. Select Polygon Property Count From GIS from the GeoPlan menu. This displays the Property Count dialog. Select the layer containing address point data:
    • The dropdown list contains all the layers currently loaded that contain valid address point data.
    • Click the Change Layers button to display the appropriate Layer Control dialog for your current map control to add the layer containing address point data if it is not currently loaded in the GeoPlan.
  3. If you have one or more polygons selected on the GeoPlan Window, you have the option of only updating the selected polygons. Check or un-check the Update Selected Polygons Only check-box.
  4. Click Do Count to complete the process. InfoWorks calculates the Number of Properties value for all polygons with the #G flag, or all selected polygons if the Update Selected Polygons Only option was checked.

Calculating from Existing Demand Data

InfoWorks calculates a value for the Number of Properties field from the Number of Properties data entered for individual nodes on the Node Demand Page.

You need to have the Demand Diagram that defines the Demand Categories used open during the operation, because InfoWorks needs to check the type of demand. InfoWorks ignores all Leakage categories, because properties included in normal demand categories may be duplicated in leakage categories.

The Population value for a polygon is calculated from Number of Properties multiplied by Occupancy Rate. So you can use a variety of people based or building based data, and get a sensible value for Population by setting a reasonable Occupancy Rate factor.

To calculate polygon property counts using existing demand data for the network

  1. Open the network containing the polygons you want to update. You may need to change the flags on the Number of Properties field for your polygons. The process only updates the field if the #N (network) flag is set. To change flags:
    1. Click the button or choose Window Grid windows New polygons window. Choose the Polygons tab. This displays the Polygons Grid View of the Polygons Grid.
    2. The Number of Properties field must have the #N (geographical) flag before a polygon will be updated by this process. If you do not want a polygon to be updated, set the flag to something other than #N. (Do not use #G as this will clear the value expecting it to be calculated from GIS data.)
    3. Make the GeoPlan Window for the network the Current Active Window.
  2. Select Polygon Property Count / From Network from the GeoPlan menu. InfoWorks calculates the Number of Properties value for all polygons with the #N flag. You may want to view the Polygons Grid View in the Polygons Grid again and check that the Number of Properties and Population values have been updated.
Parent topic: About polygons

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