(While I'm waiting for the numerous annoyances of .19 to be fixed, I'm sticking with .18, so keep that in mind!)
I usually play on large regions (257x257), tinkered to make things appear just how I like (more wetlands/forests since I like relatively flat embarks) Typically, I generate a couple of worlds and go on my merry way.
However, I'm trying to make a smaller, faster world (and fort) this time to help avoid the issues with FPS that set in around the 100-150 dwarf mark. (My most recent fort is ~130 dwarves and while it's not FPS death, it's getting noticeably slow.) As part of this, I'm trying to create a smaller (65x65) region. When I do so, I'm getting an error I've never seen in my large regions. The wiki either doesn't explain this one, or my search-fu is weak (or both).
The common error is: "The Dimensions of Dawning, region2: Flat/rough areas not evenly distributed: 2570-1627-28" and I'm generating hundreds of worlds where 80-90% have this error (with different unequal distributions).
I've got no limitations on elevation, and I can't see a way to alter the distribution of flat/rough directly. What am I missing? Where's my setting handle to alter this so they're not all rejects?
My settings for this world are listed below, for reference:
[WORLD_GEN]
[TITLE:CUSTOM SMALL]
[DIM:65:65]
[EMBARK_POINTS:1274]
[END_YEAR:1050]
[BEAST_END_YEAR:100:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:1:400:101:101]
[RAINFALL:18:100:101:101]
[TEMPERATURE:45:75:101:101]
[DRAINAGE:0:66:101:101]
[VOLCANISM:0:100:101:101]
[SAVAGERY:32:100:101:101]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[MEGABEAST_CAP:5]
[SEMIMEGABEAST_CAP:10]
[TITAN_NUMBER:5]
[TITAN_ATTACK_TRIGGER:80:0:100000]
[DEMON_NUMBER:22]
[NIGHT_CREATURE_NUMBER:22]
[GOOD_SQ_COUNTS:24:252:480]
[EVIL_SQ_COUNTS:2:20:40]
[PEAK_NUMBER_MIN:1]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:2]
[REGION_COUNTS:SWAMP:66:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:264:0:0]
[REGION_COUNTS:MOUNTAINS:528:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:528:0:0]
[REGION_COUNTS:HILLS:528:0:0]
[EROSION_CYCLE_COUNT:250]
[RIVER_MINS:25:25]
[PERIODICALLY_ERODE_EXTREMES:1]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:2750]
[CAVERN_LAYER_COUNT:1]
[CAVERN_LAYER_OPENNESS_MIN:0]
[CAVERN_LAYER_OPENNESS_MAX:1]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:1]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:1]
[CAVERN_LAYER_WATER_MIN:1]
[CAVERN_LAYER_WATER_MAX:100]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:15]
[LEVELS_ABOVE_LAYER_1:5]
[LEVELS_ABOVE_LAYER_2:5]
[LEVELS_ABOVE_LAYER_3:5]
[LEVELS_ABOVE_LAYER_4:5]
[LEVELS_ABOVE_LAYER_5:2]
[LEVELS_AT_BOTTOM:1]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:5]
[MOUNTAIN_CAVE_MIN:6]
[NON_MOUNTAIN_CAVE_MIN:12]
[ALL_CAVES_VISIBLE:1]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:10]
[TOTAL_CIV_POPULATION:15000]
[SITE_CAP:264]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:0:0:0]
[RAIN_RANGES:0:528:264]
[DRAINAGE_RANGES:0:528:264]
[SAVAGERY_RANGES:0:528:264]
[VOLCANISM_RANGES:264:528:264]
Locking: Found it. Drainage was my culprit. Setting maximum to 80 allowed it through.
Diagnosis:
1. Turn off map reject logging.
2. Run ~1500 maps through worldgen until drainage reports as the culprit.
3. Adjust drainage upwards to allow some high-drainage areas.
Note that the error message is not indicative of a problem with drainage!