Is there a way to set specific rules when creating a thematic map in MapInfo? I would like to exclude the polygons that have too many of the items I want to represent from the thematic map (something like "restrict dot density map to polygons with population < 10000").
You can use a dedicated expression that will set values below a certain threshold to 0 and keep the remaining values as they are.
I have typically used this for labelling rules but it can also be used for thematics using the Expression builder.
The expression would look like this:
- COLUMNNAME is the name of the column holding the values you want to create the thematic based on
- 50000 here is the threshold used. You can use any value
You can use any expression to exclude certain records from your thematics. So you don't have to use the same column you are using for your thematics and you can also use a different operator than >.
You can query your table, add the result to the map and add the thematic to this query.
In this way, they thematic will only look at the data in the query.