Below the table I have created with the # of tiles for each combination of Road (R), Grass (G), City (C) on the 4 sides of a tile.
You need to consider the tile rotation, so the order in the table considers in the order: Roads, Grass, City and proceeds clockwise. It seems complicated, but it is not if you look at at a tile, and imagine it rotated with the road at the top and then look at what is by it clockwise and so on.
If you think a combination is missed, it is likely it exists in a rotated form (i.e. I am pretty sure i have not missed any), so look for it .
It does not discriminate on what inside the tile, so a full city tile or 4 city border (each one on a side) tile are considered exactly the same.
The table helps to decide how likely is to have a tile of a certain type to close cities or prevent it and so on.
Hope it helps and happy to receive comments.
I was trying to add the actual tile pictures in any row, but I could not find them in a separate and easy to use form (total tiles are available here: http://mlab.taik.fi/~apaterso/projects/ ... -toups.pdf ). If you know where I can get it I am happy to include them.