Topic: Map Editor - As of 03/07
Really cool so far! Time saving & user friendly tools are a nice touch.
Some suggestions. I might just be missing how it works, or how to add it in the resource editor, if it it is supported.
For the Tile Sets, I wonder if it's possible to add variants with randomization. For instance, this ground set has 5 variants of the fill to reduce repetition. There are many floor tiles like this where they look best randomized. The same might go for the various (, <, and \ variations as well. I imagine in the long run we could use the larger resolution textures and generic alpha transition tiles with redone draw code.
Alternatively, or in addition, could the fill tile be larger? That might aid in reducing the repetitive look. So long as the tile is seamless, and WxH is correct multiplier. For example, the fanning cobblestone is 3x3 - 9 separate tiles. Painstaking to place it properly. 
I wasn't able to place ground object art as wall tiles. Are they meant to be placed as walls?

Would it be workable to introduce some granularity to the X,Y,Z placement within the placement coordinates? Maybe pixel or other small set increments within a reasonable range to keep it inside the coordinates. Increasing the placement variability would let us for example place a pickaxe on a table vs floor of table. (e.g. placing the pickaxe at X=302(-16) Y=371(0) Z=0(+30) with the parentheses value being in pixels would bring it up off the ground and on the table, and slid over so it's not hanging off the table defying gravity) Having everything centered at the bottom tile often doesn't look right. Even most of the 2nd layer wall decals, or standalone decoration wall tiles.
I suspect this is not an easy change. So, if you get to a point where you're considering new format. Along with map sizes, and other properties I hope you consider more granular placement of things.
The green box placing preview is nice, but it kinda overloads me visually for some reason and makes it hard to tell what size you're placing. I'd suggest having more contrast to the "bottom" preview color:

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