Options for Allocating Polygon Data
When different polygon groups cover the same area, allocating data associated with one polygon group to another is a common task in spatial analysis. TdhGIS provides several options for accomplishing this task and the tutorials provide detailed instructions for each option. This is a discussion of when each option might best be used.
For allocating just one data type at a time, there is a straight forward operation. Polygon data include a field, user_data, that can be populated with any user supplied data. For a discussion on options for populating this field, see the tutorial “Setting the User_Data Fields”. Once the 2 Polygons groups exist and one group is populated with user_data, the data can be allocated to the other group simply by selecting Operations | Allocate Data | Polygons to Polygons as described in the tutorial “Allocate Data from Polygon Group to a Polygon Group: Method 1”.
For allocating more than one data type, there are a few options.
For a one-off task, repeatedly using the Allocate Data operation for one data type at a time may be a suitable option.
By placing the data in an Sqlite database, the Overlay operation can be used. This is a good option if there is source data from both polygon groups that should be merged into an intersection polygon group. Overlays allow data to be allocated based on area or ascribed directly from the source data (attribute). Data filtering is also supported. The Overlay operation performs the sophisticated join queries needed to populate data for the intersection polygons. If it is desired to aggregate data for one of the original polygon groups, a simple user query may be used. Overlays are discussed in the tutorial Overlays.
By placing data in any database manager, user supplied join queries may be used, along with any desired filtering. TdhGIS will supply the necessary information from the spatial analysis, i.e the Intersect Polygons operation. This approach is also suitable for merging data from different polygon groups. This approach is discussed in the tutorial “Allocate Data from Polygon Group to a Polygon Group: Method 2”