Bleh, posted some stuff in the other thread then saw this was a double post If a mod wants to move that stuff into this thread then please do.

Your best bet is to sit down with a pencil and paper and work out how big you want this map to be, where it starts, where and HOW it moves to the next map ie. some significant event in the battle that makes people move, if it's mass combat then this is going to be a retreat/strategic retreat that can move an entire army, otherwise players might get the idea of going wherever they want. Once you've designed it on pencil then work on it digitally.

If you are going for a large scale map then there are few things to take into consideration:

1) What is the largest distance your attackers can fire from in ranged combat? If they can shoot 30 Squares then you need to keep this into consideration otherwise you end up in a situation where your ranged tokens are on one map when they retreat and your melee guys on another.... confusing Touching on the above I've worked with a map where the grid squares were 25x25pix, any smaller and you start to struggle to see the tokens. The larger your maps grid obviously the longer it takes to load in a session. If you do go for 25x25 then you can get a 100x100sq map (2500x2500pix) which is big, but not TOO big imo for one image. If your battleground is going to be bigger than this then consider how you want to break it down.

2) When designing the hills don't worry TOO much about the details of smaller hills because they wont matter too much to the battle. The larger hills that actually affect movement, etc. are more important when it comes to the look of the map and determining what terrain is leveled out, etc. The example you have made, whilst nice, might be a little confusing during the session. Large scale battle maps really do work better if they're simpler (in my opinion anyway).

3) Think about larger terrain features like buildings, trees, walls and rocks and where they would be situated (for realism and also to be best used during the battle. If there is a feature you really want to be used then obviously the best place to put it is smack bang in the middle of the map as that is where everyone will drift to). From there add in small details as needed (again, depends on the scale/view distance of the map).