It isn't pretty, but it's starting to become a little bit functional.
AND HERE IT IS, PATRONS! (Previous comment is emphasized)
The editor takes the brush that you choose by clicking on a tile to the left, and 'paints' it into the array which represents the map. All you need to do is click in the viewable area (which can be scrolled around per-pixel, since the map is larger than the edit window) and drag your mouse around to paint tiles inside.
I'm currently working on creating brush types and sizes. Thus, you can paint tile-by-tile, or a 2x2, 4x4, 8x8, or 16x16 'square' or 'circle' of tiles at a time.
Edit: Most of today's work went into code optimizations. This is essentially how I code in general. I can break my coding time down like so:
20% - Write the base code, make sure it works properly.
60% - Optimize a large chunk of code that has nothing to do with what I'm working on at the time being. These optimizations just pop in my head while I'm coding, and I immediately stop what I'm working on, and make the changes, so I don't forget later on.
10% - Idiot-proof the code, so nothing can go wrong. I've become so used to thinking about coding this way that it's drastically reduced in coding time, since I now just naturally think of the possible errors first before coding. This has made life easier.
10% - Throw in some 'glitter' code, which is essentially little ideas that usually form the foundation of a new 'base code'.