Note: this article is not applicable to M2TW - the problem appears to have been resolved in that game.
In Rome - Total War and Barbarian Invasion there can be problems if you have too large a map with too little land (or too much sea depending on how you look at it). This was initially thought to be an issue of a required hard-coded ratio between the amount of land and sea. Subsequent experimentation has shown that this is not the case.
For some discussion on this issue see here.
Attempting to load a newly designed or re-sized campaign map gives a CTD without -show_err message as soon as you select the arrow to launch the campaign from the faction selection screen. A new map.rwm is NOT generated. Also, in the root folder, a new cliffs_debug.tga is created. corrected_regions.tga is NOT created.
Umm, well it seems to be to do with path-finding!
There is no ratio involved in this problem at all. Too large an area that land units are excluded from produces crash. This becomes more of a problem for larger maps as it is easier to have too large an area.
It has not been possible to exactly define 'too large an area'. There is no figure in terms of actual area, height or width! What is not possible can only be found by experimentation for each size of map and coastline layout.
Even within the same sized maps, no ratio can be discerned. A map with a lot of small seas can have far greater ratio of sea to land than one that tries to have only one larger sea. The shape of the sea also has an effect, with simple plain shapes apparently being the hardest to accommodate.
Relationship to Impassable Terrain
If you substitute any of the impassable land terrain types for areas of sea which do not work on the map, then you will still have same problem. Impassable land terrain types include the forest and mountain types. Including a VERY large area of forest or mountain gives exactly the same crash as having too large a sea.
If you add an island to break up sea area and make it's terrain entirely impassable you will gain no advantage. If using a land-bridge or definite link between land masses to divide sea solves initial problem, then attempting to make that bridge impassable by use of forest or mountain terrain will bring back the CTD.
- Make map smaller, a sea shape that won't work on a large map can be perfectly fine on a smaller map.
- Add islands that aren't actually required for campaign, in the form of 'graphics', they can be isolated by placing 'ocean' ground type around them if necessary.
- Try tweaking the sea shapes, reduce widest areas and make narrow points even more narrow, sometimes almost but not quite divided seas can work. Seas that are divided but remain accessible to ships by use of land-bridges can also solve a lot of problems.