All about terrain.
G - shows map grid, terrain types and how Impeded the terrain is.
N - shows terrain height and type.
It determined by numbers (0, 1, 2 etc). Terrain height means you can't move across a number (eg from 0 to 2, or from 4 to 1), champions without special abilities like Flight or Mountaneer can move only one height number higher\lower at the time.
Related abilities: Flight, Climb, Mountaneer, Ethereal, Creep and Crawl...
Some types of terrain can be Impeded. It means a champion without special abilities related to Impeded Terrain will waste 1 or 2 more AP to move through it. Terrain can be Slightly Impeded (means to move through champion will waste 1 more AP), or Impeded (2 AP).
Related Abilities: Flight, Mountaneer, Ethereal, Arctic, Amphibious, Aquatic.
Terrain can be impassable, which means champions without Flying or Mountaneer can't move through it. If the champion loses Flying while occupying Impassable terrain it will suffer 5 physical damage each turn and be not able to move.
Basic terrain types are:
Chasm - deadly terrain, any champions without flying that occupies chasm will die instantly. Large champion can occupy up to 2 chasm spaces without dying.
Notes: champion can't be blinked if it occupies Chasm.
Related abilities: Create Chasm, Chasm Walker.
Related spells: Lay Bridge
Earth - has no icon if map grid is activated. Tunnel Earth can be used on any of its' sub-types.
Related abilities: Tunnel Earth.
Vegetation - favored by Kthir Forest.
Related abilities: Tunnel: Vegetation, Domain: Vegetation, Hidden: Vegetation, Plant Regeneration, Camouflage, Trail: Vegetation, Forest Walker.
Rock - favored by Ironfist Stronghold.
Related abilities: Tunnel: Rock, Domain: Rock, Hidden: Rock, Surge: Rock, Trail: Rock, Rock Front.
Related spells: Macadamize.
Dirt and other ones - generic Earth terrain.
Water - has a water symbol if map grid is activated. Can be Impeded. Favored by Forglar Swamp.
Related abilities: Amphibious, Aquatic, Dive, Domain: Water, Hidden: Water, Trail: Water.
Related spells: Monsoon.
Snow - has a snowflake symbol. Can be Impeded. Favored by Savage Tundra.
Related abilities: Tunnel: Snow, Arctic, Domain: Snow, Hidden: Snow, Trail: Snow.
Ice - has an ice symbol. Champions on it without certain abilities will suffer -1 SPD debuff. Favored by Savage Tundra.
Related abilities: Tunnel: Snow, Arctic, Flight, Trail: Ice.
Related spells: Ice Storm.
Tar - has no icon. Always Impeded.
Related abilities: Flight, Ethereal, Mountaneer.
Lava - has a fire icon. Always Slightly Impeded or Impeded. Deals 4 damage to any champion without Flying that moves through it and to any champion without Flying that occupies it at the beginning of its' turn. Favored by Underdepths.
Related abilities: Flight, Lava Walker, Trail: Lava, Terraform: Lava.
Sand - has no icon. Favored by Sundered Lands
Related abilities: Tunnel: Sand, Trail: Sand, Hidden: Sand, Domain: Sand.
Ooze - has no icon. Favored by Slags.
Related abilities: Ooze Tap, Trail: Ooze, Oozing.
Terrain can have some additional effects on it:
Hallowed Ground - at beginning of your turn, Undead and Demon champions as well as Forsaken Wastes and Underdepths relics in this area lose 2 life, Priests, Shamans, and Paladins are cleansed and healed for 8 HP, and terrain modifications are removed from this space.
Related abilities: Trail: Hallowed Ground, Consecration.
Related spells: Consecrate the Earth.
Desecrated Ground - at beginning of your turns and upon casting Non-Undead Champions in this area lose 6 life.
Related abilities: Desecrate Earth.
Dead Magic Zone - enemy spells can't be cast in friendly Dead Magic Zone. Favored by Forsaken Wastes.
Related abilities: Hidden: Dead Magic Zone, Shadestrike, Desecrated Zone, Cast: Despoil.
Related spells: Dead Zone Voodoo, Drain the Earth, Despoil.
Unstable Ground - champions without flying in this area will suffer 5 physical damage for each space its' moved and at the beginning of each turn.