Oblivion CS' heightmap editor requires a 1024X1024 file for importation. This I have accomplished, but I intend to make the scale realistic.

What is the scale of one pixel in the height editor in terms of real-world units (feet or meters)? Or, failing that, what is the scale, in km or m, of the 1024X1024 tiles that oblivion uses in the heightmap editor?

You can work out something rough by knowing:

• Toggling the grid lines in the Heightmap editor enables you to see specific cells (Each box is a cell)
  
• There are 64 grids (box bits), therefore 64 cells, in each area of the 'Overview Window'
  
• As this show, the Overview Window is an 8x8 matrix
  
• That means there must be 512 (64 x 8) cells along each side of your 1024x1024 square

If that's true, then every 2 pixels are a cell; which seems stupid. If you take a screenshot of the heightmap editor with it's gridlines on, each grid/box takes up 10 pixels by 10 pixels.
So the conclusive answer is - I don't know exactly; but the Wiki tells us:
The CS says there are 11,926 cells (in a 134 by 89 grid) in Tamriel (although a lot of them won't be accessible, due to the Region boundaries).
I'm not sure if that helps at all or not, but a 1024x1024 heightmap will mean you need a 1024x1024 map to go ingame; and Tamriel (all of the map) uses a 2048x2048 map (although some of this isn't viewable, and it shows bits of the border regions anyhow).

Good luck. I'm not sure if I've actually proven anything at all; just quoted numbers to you. Hope it helped, somehow!

Edit: Should have read the whole post above mine, but I still think it should be 128x128 units per pixel. I've imported a heightmap once and in some areas you have those little jaggies, something that can't happen if one pixel is more than 128x128 units. That would mean (128x1024/4096)^2 = 32x32 cells per 1024 pixels or 1 quad per 1024 pixels.

EDIT2: It would make more sense if one pixel is one vertex with a distance of 128 units between the vertices. Just to put it correctly.

Ah, that makes sense if each pixel is 128 units; since each vertex in the terrain is 128 units (give or take) apart. That would mean every 32x32 pixels is a cell. That also means there's a 32 by 32 cell matrix in each 1024x1024 terrain map.

Cheers Phitt!

Thanks, that will be useful information when I implement this, but I need an idea about how to convert oblivion units into real world units. I need to know what the equivalent of one pixel (regardless of how many units are in a pixel/how many pixels are in a cell/etc) is, in feet or meters. For example, if you were to describe an npc's height in units, what would the equivalent be in feet (or better yet meters?)

The average character has a height of 128 units (~1.83m), a cell has 4096x4096 units (58.5m). A quad is 32x32 cells (1.87 km^2).

Brilliant. Thanks!

Just be aware that trying to do any real-world location to scale would probably not work very well due to how you would need several quads worth of terrain just to create a small town. The whole continent of Tamriel in TES4 is actually smaller than the large island of Hawaii, and building a worldspace larger than 4x4 quads is not particularly suggested.