This was just an in-house tool that I needed to help create geographic boundaries for a location service I wrote. There are a number of public domain and open source map repositories but they are often in different formats and/or contain information unnecessary for this project.
The first use for this tool was to create usable DMA data. The official Nielson DMA data did not include navigable waters or coastal waters. This led to people at docks or out fishing who were incorrectly identified as not in a DMA. You can see in the screenshot that the DMA data closely follows the coastline, where the county swallows that into a smoother extended region. More useful, and quicker to process!
The second use for this tool was creating usable geographical data for China. The maps I could find where either to simple, or to complex. This tool let me simplify high-accuracy coordinates to reasonable paths. Again, coastal islands were merged into the various coastal regions.
Lastly, countries were loaded into the database and subregions of business interest to this customer were sought and added. A few days work to create the tool, and one serious migraine avoided.
The interface is not very refined, but I was the only one to ever use it. Just the way a tool should be. Just what the user needs and little more. In this case, it was easy to understand what the user needed. That is not always the case.
When a selection is made in the upper left corner, then the corresponding boundary map is loaded into the primary layer and displayed. Also, sub-boundaries are listed below the boundary popup. Country will show States, States will shows Counties. AKA 1st, 2nd and 3rd divisions. DMA is an independent list of boundaries.
In the screenshot here, the West Palm Beach- Ft Pierce DMA is loaded and placed into the background layer, and the Martin, FL county is displayed over it in the primary layer.