Depending upon where the "ambush/field army fighting" takes place (tile), determines what map is used in combat.
Vary simple, wherever the attacking army meets the counter-attacking force, based upon that tile it happens on uses a specific map. So if you fight on a planes tile, you fight on a planes map. if you fight next to a body of water, you use a map next to a body of water, exa. In doing so you provide a visual variety to the fields of combat in that mode. Not like these maps have to be that detailed.
Example, Open fields/low hills: use that map you teased us with the broken cart in the center and flat lands.
Forrest: per say there is a mostly straight fairly wide, well traveled road going forwards, both sides of the road has forested areas. Perhaps maybe there is a hut or two in the forest/just off the road (a small homestead with a small field?), some short stone walls on the side of the path. Maybe a stream somewhere with a teeny bridge. That simple.
Mountains: Perhaps we can have a main cobblestone road going along a steep and dangerous mountain range, perhaps in the middle is a wide precarious bridge with some less than ideal railing structures over a ravine with a decorative tributary. There may be several smaller footpaths leading around (that also lead close to the opposing forces spawns) so people can maneuver around, rocks spotting the area providing cover. Here you need to be aware that the enemy can be anywhere. Perhaps on several points there is a short ledge over the paths that opponents can hide on and jump unto unsuspecting foes. Complete with classical mountain tops, trees, and maybe a secluded spring or cave.
Near lake: Perhaps a rather smooth map that has a wide road with pleasant wooden fences that follows a lake along it's edge. Perhaps around the center a inlet is formed and it curves around that. Of course a dock or two may be included with some fishing decorations and crates. Some farmlands along the edges alongside some spare trees and lush grasses would be nice. Ideally the lake would seemingly take up half of the visible map. Or at the far side is some distant land.
I'm pretty sure its likely you will just do the random selection map thing, but please don't and consider this possibility. Also... having three more possible "ambush/field army maps" would be nice to experience.
Anyone with me on the general idea of where the conflict takes place determines the field of battle?
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