BASIC GAME TERRAIN CHART (6.1.2, 7.2.2)
Terrain MOVEMENT COSTS a.

USUAL COMBAT
EFFECTS (7.2.2) b.

Fortress City
1 -2 Armor; +2/+3 Other Defenders c.
Major City
1 -2 Armor; +2 Other Defenders c.
Clear
1 No Effects
Forest
2 -1 Armor; +1 Other Defenders.
Mountain
2 -2 Armor; +1 to +3 Other Defenders d.
Marsh
3 -3 Armor; +1 Other Defenders.
Hex H16
1 +4 All Defenders
Kerch Strait
Axis +3; Soviet +1 Between hexes D17, D18, E18, E19 (6.1.5)
Railroad/Oilfield
Also see other terrain in the hex. See other terrain in hex.
Minor City
See other terrain in hex c.
River
+1 Defenders.

Lake Hexside
Sea Hex

Air units only.  

CHART NOTES:
a: Air unit movement costs ar "1" per any hex.

b: Applies only to ground units. Terrain does not affect air unit attack or defense factors. All modifiers are cumulative, but not attack or defense facto is ever reduced to less than "1".

c: Maximum of two air units per airbase (4.3) 

d: Cavalry units are "+1" defending, mountain units are +1 defending, all others (except armor) are "+2" defending (7.2.2.5).