I have access the full data set of the KML file shown here: http://www.maptechnica.com/downloads/samples/mt_2014a_kml_us_zcta5_sample.tar.gz
Here's what it basically looks like: http://www.maptechnica.com/us-zip-code-boundary-and-geodata
It's basically a bunch of polygons that match (close enough) ZIP code boundaries. What I also have is a table that shows which zip codes go with which territory (i.e., a territory overlaps multiple ZIP codes).
I'm looking for a tool that I can use to merge these two sources together to create new polygons consisting of the group of zip code polygons that make up a territory.
Mapping is completely new to me, so I'm not even sure which tools I need to use.
Ideally I'd like to avoid making a big software purchase.