Setting Population Values from GIS Data

Subcatchment population data can be imported from a GIS layer containing address point, seed point or census data.

The layer must be the correct type for your current GeoPlan map control:

Please refer to the GIS Layer Control Dialog topic for the full list of the supported formats for each map control.

Note

Population data can only be imported to a network that has subcatchment data for boundaries and runoff areas.

The best form of data is data with one point per address. Seed point data is less good as it will often contain a seed point per building, giving the same weight to a house and a block of flats for example. It may also include non-residential buildings.

These address points or seeds could come from several sources:

  • Local Authority population data
  • Building seeds (points representing the centres of buildings) from a DXF file

The GIS layer must contain point data. These points generally represent a person, an address point or a building. If using address points or buildings there are two ways you can calculate the final population figure:

  • Load a population figure for each point from a data field in the GIS layer. This field can be selected during import
  • Enter a multiplier representing the average number of people per household during import

Census data takes the form of polygons representing census regions. For each polygon there should be a corresponding data field containing the population information.

The population taken from each polygon by each subcatchment should be in proportion to the area of the polygon which lies within each subcatchment. In other words if a polygon has a population of 200 and 70% is in subcatchment A and 20% is in B (polygons can have areas that do not apply to any subcatchment) then a population of 140 from that polygon should be applied to subcatchment A and 40 to B.

When setting population values, the following rules are followed:

  • Only subcatchments with Populationfield flag set to #G will be processed
  • If network subcatchments overlap, the population contribution is only applied to largest subcatchment
  • Overlapping subcatchments also increment the Number Blocks value in the summary table
  • If GIS layer polygons overlap, the population contribution from both is applied

Setting Subcatchment Population Values from GIS Data

The GIS layer can be loaded onto the GeoPlan in advance, or the file can be accessed directly without pre-loading.

To pre-load the GIS layer:

  1. Right click on the GeoPlan Window and choose GIS Layer control from the popup menu. This displays the GIS Layer Control Dialog.
  2. Click the Add button. Choose the theme containing the population data (address points or census data) in the File Open dialog.
  3. If the data is not displayed on the view, right-click the GeoPlan Window and select View entire GIS layer
  4. In the View Entire Layer dialog, select the layer and click on OK.

Only subcatchments with population fields set to flag #G (Geo) will be updated.

To set the #G flag on the population field of subcatchments:

  1. Click on or choose Grid windows | New subcatchments window from the Windowmenu to open the Subcatchment Grid Window of the Subcatchments Grid.
  2. Select the entire Populationcolumn and right click on one of the selected cells. Use the Flags option on the popup menu to set the flag to #G. This will change the cells to the #G colour and delete existing values. To set the #G flag for a selection of subcatchments only:
    1. Select subcatchments to be updated
    2. On the Subcatchment Grid View of the Subcatchments Grid, go to the Grid menu and choose Group network selections at top of grid.
    3. Now go to the Populationcolumn and select the population cell for all the selected subcatchments. This will not change the subcatchment selections.
    4. Change the flag for the selected cells to #G

To update subcatchment population fields with address point or census data:

  1. Ensure the GeoPlan Window is the active window and choose Subcatchment | Population data from address point counts or Subcatchment | Population data from census areas from the Model menu. This displays the Subcatchment Population Dialog.
  2. On the Subcatchment Population Dialog:
    • Choose data source file and file field containing population data
    • For address point data set a fixed value multiplier (people per address) or choose to use the value in the GIS data field
    • Select whether to update all subcatchments or currently selected subcatchments only
    • Set a flag to be applied to updated fields
    • For census data set reporting options
  3. Click OK to complete the data import process. The population for all (selected) subcatchments will be updated.

Subcatchments

GeoPlan Window

Subcatchments Grid

GIS Layer Control Dialog