I would disagree with the statement that map is rendered with 2d methods, it perfectly looks like this was done under heavy usage of d3d methods.
Let me start with a 'what would I do'-example to achieve a more modern aproachment in mapping technique:
first, see what they already have:
- A map format, already in use.
- a client and a whole server architecture, they'll have to stay compatible to
- lots of tools
means: there should be as less changes to other systems as possible with the biggest amount of changes in using/interpreting those files and formats.
'Old UO' uses a very modest way of drawing a map by concatenating tiles one to another. As we know, this way affords that transitions between different tilesets (grass<->dirt) needs own transition tiles and various tiles are needed to create a scene that doesn't obviously look repetetive. So we also have 4 or more tiles of grass just to create a field that doenstn look mechanical.
More modern appraoches to receive the same result is to use just _one_ splatting texture over a bigger field of tiles that should look the same. Imagine it like playing LEGO. The old way was to lay many many little blocks right to each other to create just a fundament, while LEGO now produces a big pane (with a nice city-scene drawn) you can build upon. Got it?
As 'we' have to stay compatible with all those old tools, the best way would be to automatically convert all tiny lego pieces with the same look to one pane. Glueing them together. So we take all tiles that have the same meaning (like mentioned 4+ grass-tiles) and reduce them to one pane that uses a higher resolution texture, so this doesnt look repetitive.
Texturizing a grid/set of polygons with a texture is a
highly optimized procedure. Since GeForce came up, this is effectively done by the GPU!
This way, they can also remove all those transition tiles
simply by overblending the panes.
This way, the new client needs just one texture per tileset instead of multiple tiles.
Now they saw their 'dirt' texture, a tileset often used to create roads in 2D, doesnt look like a road anymore. So they created a new one, 'road stone', adding one new tile, patched this right into the map and it looked wonderful in KR.
So they decided to add the graphics to 2D as well to stay compatible, chopped them to different tiles to avoid that repetitive look.
But the map still contained one single tileid as KR just needs 1 to address the whole texture with transitions.
Thus, it looks ugly with 2D.
Last comment: I don't know how it it is done at last, but for me, this seems to be the method of choice with the best performance- and effort-tradeoff