MapWindow:Desktop:UpdateMeasurements
From MapWindow GIS
Create or Update Length, Area or Perimeter Attributes
The Update Measurements tool is an additional plug-in which allows users to calculate line length or polygon area and perimeter, and add these to the attribute table. Users will need to download the plug-in and switch it on. This installs the Update Measurements 
icon on the toolbar.
Calculate Line Length
To add a field in the attribute table which contains the length of the lines;
- Click on Update Measurements icon
- The Update Measurements box appears
- Select the layer to update from the list
- Select the correct shapefile units (if not already populated)
- Select the units for the calculations to be made in, ie Meters, Kilometers, Feet etc
- To use an existing field in the attributes, select ‘Existing’ and the field name from the list
- To create a new field, select ‘New’
o Length will be added by default to the name, or rename to preferred
o select the number of decimal places
- Click [Update Measurements] button
If further layers are to be updated, then repeat as above, or click [Close] button to close box.
Calculate Polygon Area & Perimeter
To add a field in the attribute table which contains the area and/or perimeter of the polygon;
- Click on Update Measurements icon
- The Update Measurements box appears, with perimeter and area calculation options
- Select the layer to update from the list
- Select the correct shapefile units (if not already populated)
- Select the units for the calculations to be made in. Note – meters is the default for Perimeter units if Hectares is selected, or Feet is the default if Acres is selected.
- For each of either Area or Perimeter
- To use an existing field in the attributes, select ‘Existing’ and the field name from the list
- To create a new field, select ‘New’
o Length or Area will be added by default to the name, or rename to preferred
o select the number of decimal places
- If either field is not required, select ‘None’ for these
- Click [Update Measurements] button
If further layers are to be updated, then repeat as above, or click [Close] button to close box.
Polygon Areas – GIS Tools option
If users only require Polygon Areas to be calculated, without the need for additional plug-in;
- Click on [GIS Tools] then click on [Vector]
- Click on [Calculate Polygon Areas]
- If it cannot detect the shapefile units a warning will show asking if you wish to use the units in the projection. Click OK
- The calculate area box appears
- Select the layer.
- Set the shapefile units
- Set the units of the area the user want created
- If this is the first time, select the 'Use a new field' and give it a new name if required
- If there is already an area field, select 'Update an existing Field', and select the field from the list
- Click on [Calculate]
Your field will now have the area calculated.
The option to specify decimal places is not in this tool. To specify decimal places, use the Update Measurements Plug-in as above.
