Firstly, it's important to establish that the extents of the map, because, while it may be possible to add to it at the top and bottom, the left and right will be fixed permanently and beyond appeal! To that end I'll provide a definite map with an overlay of coastlines and rivers.
The next step is going to be to create a basic ground and height map. These map will only have 3 terrain classes: Land, Beach and Sea. Getting the coastline right is the main challenge here.
Once that is done, the regions map can be implemented. I can do this, but help would be welcome. The historical geography of the map should be laid out fully and accurately before the ground types are developed further and even the height map needs to take this into account. That concerns the placement of settlements, ports, roads and sea-lanes. Of these, settlements and ports can best be done by collecting their latitude and longitude in decimal degrees in a spreadsheet, so if anyone wants a job, compiling that list would be very welcome.
With a basic division of land and sea and a regions map, we'll have the first "test-able" map. Characters will have to be commented out or moved temporarily.
Next up will be the features map. Lots of manual editing again.
After that, we have enough info to build the land portion of the height map. Areas under settlements will need to be smoothed and, always fun, the terrain needs to be adjusted under the rivers to ensure they run downwards nice and gently.
Next up, the climate map. This is easy in a sense, as it does not materially affect anything except looks. However, solid info is hard to come by. We know Africa and the middle east were somewhat more habitable. Perhaps we can use ancient settlement patterns as proxies.
The ground types map is to be constructed last. The ground under settlements and roads has to be reserved for passable ground types. Otherwise, terrain slope will inform where to put mountains, hills or arable land. This is rule-based and those rules will vary depending on the climatic zones. This process is basically done with a script.
Seems a bit daunting, but I've documented most of these steps well enough.
