Drain room amounts per room type
95 skills, 90 drain room, 241 int 

jungle/valley:              84sp
fields/deep forest:         66sp
forest/plains:              34sp
highlands/swamp:            22sp
pcity:                      16sp
beach:                      2sp 
river/sea/shore/ice fields: no magic
shoreline/ruins/tundra:     -5sp
desert:                     -10sp !

Trees and deposits give extra sp

gems:                       +50sp
trees/herbs:                +25sp
metals/stone:               +20sp