Map Randomisation

I was recently thinking about how I could generate a playable random map for my tile based strategy game. I can foresee many difficulties with this. Below is a sample map created in the map editor:

This map although not very well balanced looks sensible. The roads are connected and features such as trees and mountains are grouped in semi-realistic clumps. The river is also continuous and flows from one side of the map to another. If this sort of result is to be achieved my a random map generator it will need to follow these rules:

• If the tile is blank there must be a chance that a feature is placed on it. This should be larger if adjacent tiles contain this feature.
• Roads and rivers must form a closed loop. (counting the map edge as closed).
If there is a road or river section in an adjacent tile and it is "facing" into the tile it must be continued.
• (Optional) The map be balanced in terms of resource and position or be symmetrical.

Ideally the chance of each feature (i.e. hills,woods,mountains) being placed in tile should be determined by an initial value and the tiles surrounding it. If this was a case the user could define the initial chances by selecting an option such as hilly or woodland before generating the map while the affect of nearby tiles could help produce the desired "clumping" of features.

I intend to try and write some pseudocode which achieves these effects soon.