Put the testing check for resource placement on the world map into its own function.  Generate the City_map using its new function.
Better comments/spacing.  New Map::generate() function, which takes a list of crops and minerals to place here (derived from the world map.  Crops and minerals only appear on a tile if it's assigned from the world OR we hit a small chance.
Mineral_amount::make_small() returns the same Mineral_amount, but with the amount reduced to 10 to 20 percent of the original.  Used for when a mineral appears in a City_map tile without being assigned by the World_map.
When placing resources, use a min/max radius dependent on the resource's appearance percentage (lower percentages have smaller radii).  Adjust the total amount of blobs depending on the average size of the radius.  Also add status popups which inform us where in the resource-placing process we are.