5.1.9 Frequency Analysis of Points
Level of expertise required for this Chapter: Advanced; general GIS training. This Chapter is available in improved version in Chapter 5.6.2; it will be deprecated here.
For a GIS crosstabulation to produce statistics how many points occur in particular areas, you overlay points with polygons (sometimes also called 'crosstabulation').
You might have to prepare your attribute source, if crosstab data are not in the label field in the DRA file):
1a. Copy source DRA file to temp DRA file
1b. Copy this temp DRA file to live layer, then Live layer actions > IDs and labels > Amend labels and IDs > OK > Set display labels equal to IDs > OK > Save live layer as... > Same name > Save
Utilities > Vector utilities > Actions > Choose DRA file of points > Open > Transform window: Spatial queries > Inherit attributes from other file > OK >
> Inherit attributes from other file window: Polygons file > Select temp DRA file (from step 1) > Open > Tick: Inherit label > OK >
> Save as window: Specify new file name (DRA file)
3. Export crosstabulation for all points:
Utilities > Database utilities > Generate database from DRA > Select file, just created > Open > Generate database window: Tick Display label > OK > Save as window: Specify new file name > Save as type: CSV > Save.
This step is also explained in Chapter 5.6 ('Export tabular GIS data').
4. Final frequency distribution in Excel:
The next steps are carried out in Excel, explained in Annex 20.2 (Excel: Frequency).