World generation

make_world() in WORLDGEN.C is overlay 7. It prepares terrain, regions, connections and potential city sites while advancing the creation pictures and text through calls to story_step().

custom_params[0..3] hold land mass, temperature, climate and age. If beginner_help selects Earth, the routine loads map.pic instead of generating terrain, then runs the common region and connection stages.

Land and climate

grow_land() and walk_land() build land through bounded random walks. The initial growth stage stops at 640 + 320 * custom_params[0] land cells. Border cleanup and later terrain changes follow, so this threshold is not a promise about the final land count.

A pass removes diagonal checkerboard contacts. Land is then assigned terrain using abs(29 - (rand_scaled(8) + y)) + 1 - custom_params[1]. Dividing this value by six selects Desert, Plains, Tundra or Arctic.

Rainfall passes scan each row in both directions. Ocean cells build a rain counter; land consumes it and can change terrain. Mountains consume extra rain. The climate parameter affects both the amount collected and random depletion. Age controls a further 800 + 800 * custom_params[3] terrain-change iterations.

Rivers

make_rivers() saves a working area before attempting a river. It traces a route and tests the endpoint and length. Accepted routes remain; rejected ones restore the saved area. The code uses terrain tests and random choices, rather than an elevation field with a general downhill-flow calculation.

Regions

number_regions() labels connected land and sea separately, merging labels as the scan finds connections. It then ranks regions by size. The fourteen largest receive IDs 1–14, with 1 the largest; remaining regions share ID 15. continent_span[0] holds land sizes and [1] sea sizes. Entry 15 is set to 1, rather than a combined area for all remaining regions.

link_land() and link_seas() build connections on a coarser 20-by-13 grid for pathfinding.

City sites

score_sites() scores Plains, Grassland and River locations. It combines food, shields and trade across the city radius, with extra weight for nearby tiles and adjustments for resources and potential improvements. The result is reduced to a small value stored at x+80 in the working page. ai_zone_places counts candidate sites by region.

This supplies later settlement decisions. It does not directly choose and found eight starting cities.