Battlearea as a separate layer

This is a copy of my Thread here

Currently

We have the campaign map where when an army gets attackers a battle area gets drawn on the map. Depending on number of units in all participating armies and if its a siege, the battel area is smaller or larger. Especially in late game it is possible to have battle areas which take half or whole continents.

Idea:

A separate battle area is generated from a smaller campaign map area, which gets enlarged as battle area. See example below. The red outline of the tiles would be the area limits in each case. Size is an example, depending on number of units it may be smaller. Smallest possible could be a 3x3 which could result in a 9x9 playfield.

Fig 1. Campaign Map (red/green dot marks army position)

The above read marked area would result in the following battle area on another layer:

Fig 2. Battle Area generated from campaign map (approximation, House is a district). Some of the light green tiles highlight the original Campaign map tile.

Rules:

• area size still depends on participating unit number, but the area on the campaign map is generally smaller
• the tile gets generally multiplied in each direction by one (basically what happend with the house tile)
• natural terrain needs some rules since in my example adjacent types are overpainted; districts trumps all though
• rivers should flow from central tile to central tile with minor leeway and shortest route with left or right tile is same number of distance (river will only be one tile wide in this battlearea but you have clear adjacency to it)

I expect the following benefits:

• generally larger battle area without blocking other stuff too much on the campaign map
• battle areas which are close to a settlement could stop at the walls and still have a large enough battlearea even in later eras
• settlement sieges should be limited to some part of the city if the city is too large (or it could be transported to the new layer wholly, both have merits...)
• battlefields do not feel cramped
• one tile reinforcement deployment should be a thing of the past
• movement of units and range actually count for something since the area can be large and is not constraint by having it on the campaign map directly
• district tiles which adds +1 cs to its tile and adjacent tiles gives a unique possibility to make garrison tiles actually a center piece with a wall around the adjacent tiles.
• no battlefield that takes up half/whole continent
• is better scalable to different world sizes (having a battle on a "small" world size results in very large battle areas in comparison to a "huge" world size)

Issues:

• probably difficult to implement something like this as an afterthought (or maybe not since it is a new layer?)
• is it possible in a seamless way? (no loading screen)
• how to exactly make the terrain generation rules? can be too complicated if overpainted... alternative is to have always a 7 sized tile group and place them adjacent to each other)
• how about cliffs when dealing with overpainting?
• attacks from outside (air strike, bombardment)? probably the "support" tab needs an update to have all units in range be show that can contribute to current battle
• how do terrain elevation behaves? could be problematic to not have it too flat

Since this overpaint some terrain tiles, and the how and what not can be too complicated, another way would be to just enlarge the single tile to 7-group tiles and place them adjacent. Since this results in holes (see below figure) it needs to be either filled up randomly by some rules or each segment needs to me moved slightly so they fit together on the battlearea.

Fig 3. Marvelous Picture by ningauble