How Create Labels (Coverage) works
The Create Labels tool is often used to create label points for a coverage that has no polygon label points.
A few special cases of User-ID assignment using ID Base are listed below.
If the specified ID Base is negative, all new User-IDs generated by Create Labels will start with the specified value and be decremented by one for each new label point (for example, a value of -10 will result in User-IDs for new label points of -10, -11, -12, and so on).
Create Labels does not check whether the User-ID number to be assigned to a new label point already exists for a previous polygon label point. This could result in the generation of duplicate User-IDs, depending on the value specified. Duplicate User-IDs are allowed but not recommended. For example, existing attributes may be different for polygons that have the same User-ID.
Once Create Labels has been run on a coverage, the new label points and their User-IDs are stored in the LAB file. However, any previously existing User-IDs in the PAT of the coverage have not yet been updated. This creates a temporary situation where the new User-IDs generated by Create Labels are not equal to the old User-IDs stored in the coverage PAT.
You can use one of two methods to make the old User-IDs and the new User-IDs equal. One method is to use the Update IDs tool (IDEdit) to change the label point User-IDs to be equal to the User-IDs stored in the PAT. The second method is to use the Build tool to change the User-IDs stored in the PAT to be equal to the label point User-IDs. In other words, when different User-IDs are encountered, Build uses the new User-IDs in the LAB file to overwrite the old User-IDs in the PAT, whereas IDEdit uses the old User-IDs in the PAT to overwrite the new User-IDs in the LAB file. You must use whichever method is appropriate.
Several specific cases are described below:
- If you are creating labels for a coverage that does not contain attributes, use an ID Base of zero and run Build.
- If you are creating new label locations for a coverage that already contains unique User-IDs and associated attributes, use an ID Base of zero and run Update IDs (IDEdit). This ensures that any additional attributes that are stored in related files using the polygon's User-ID will not be lost or mixed up.
- If you are creating new label locations for only some polygons in the coverage, specify an ID Base value that is greater than the highest existing User-ID. This ensures that the new label points that are generated for any unlabeled polygon will have unique values. Use Build to assign these new User-IDs to the unlabeled polygons. In this case, all of the previously existing User-IDs and their associated feature attributes will be maintained.