Edit: It is not my intent to make creating stamps look difficult. It is very simple. This is a very technical walkthrough for those interested in the behind-the-scenes and to get some ideas on how to design well-functioning stamps.
I've been tinkering with stamps since way before release (in XML) and now that the map generator is out with a Stamp tool I thought I'd chip in and talk about what stamps are and why they're important.
What are stamps?
Stamps are pre-built pieces of maps that are used when a map is randomly generated. Think of stamps like Puzzle pieces that make up the total Puzzle (map) when put together. Here is a Small stamp in the Cartographer: http://i.imgur.com/4CLVN.jpg
Why are stamps important?
Because stamps determine what Random maps look like, they play a crucial role in several ways:
Visual Appeal: If you saw an area in-game that consisted of 19x19 Plains tiles, all brown, you would not be impressed. A stamp is an opportunity to give an area of the map character - why not a volcano?
Good gameplay: Starting positions, natural chokepoints, proximity to secondary and tertiary city locations, terrains like Forests and Rivers.
Replayable game: By combining (and rotating) stamps differently, every random game produces a random map which increases the fun of replaying the game.
Let's get technical. How do stamps work exactly?
There are different sizes of maps - Tiny, Small, Medium, Large (and Tactical maps, which are not randomly generated and not covered here).
Each map size consists of a certain number of sectors. I have printed the sector count out below for your convenience. From each number subtract 1 for the final count. Also note that one sector is commonly blocked by a Cloth Map compass (silly, but there it is).
Tiny Map: (Width 4) * (Height 3) -1 = 2*3 -1 = 5 Sectors.
Small Map: (Width 5) * (Height 4) -1 = 4*3 -1 = 11 Sectors
Medium Map: (Width 6) * (Height 5) -1 = 5*4 -1 = 19 Sectors
Large Map: (Width 7) * (Height 6) -1 = 6*5 -1 = 29 Sectors
Here is a Tiny map, divided into sectors (also notice the Compass taking one sector): http://i.imgur.com/aZ554.jpg
Here is a Small map, divided into sectors: http://i.imgur.com/3nGjg.jpg
Each sector consists of 16x16 in-game tiles
Edit: Note that maps are technically larger as per https://forums.elementalgame.com/435333/get;3264664. But the above list is the relevant list of sectors for the purposes of random stamp placement.
If you paid attention when looking at the sectors above, you should have noticed something odd. Certain map features such as the Arctic wildland stretch across multiple sectors.
This brings us to how Stamps are structured. Stamps come in different sizes. They have padding on their sides so they are slightly larger than sectors, this helps improve how they merge (see Stamps Merge)
A Small stamp covers 1 sector, 19x19 tiles.
A Medium stamp covers 2 sectors, 19x35 tiles
A Large stamp covers 4 sectors, 35x35 tiles
A Huge stamp covers 6 sectors, 51x35 tiles
You'll notice, of course, that the numbers don't quite "add up" to the size of sectors. I will talk about this later on when discussing how "Stamps Merge".
(there are also custom-sized stamps, wildlands. They aren't quite the normal size of stamps)
Maps and Stamps combined
In CoreMaps.xml we find more details to how exactly Stamps get put into random maps. The XML below is from Tiny map:
So, we see here that a tiny map appears to be limited to Small stamps and Medium stamps. Don't be confused by those tags, by the way (they lost the names in translation). Small stamp = TinySeedSpawns. Medium stamp = SmallSeedSpawns. Large stamp = MediumSeedspawns. Huge stamp = LargeSeedspawns.
In addition, a tiny map appears to be limited to 2 of each. So, here's an example of a Tiny map: http://i.imgur.com/bBdJZ.jpg
I have manually placed a Small Stamp (1 sector, yellow outline) and a Medium stamp (2 sectors, green outline).
Stamps Merge (and clever Stamp design)
A normal randomized (tiny) map does not contain 5 sectors separated by water. The Stamps merge together at their edges.
This presents a problem that a maker of stamps must face. How do stamps merge together at the edges? They merge together by clever Stamp design, and some background coding when randomly placed. Clever Stamp design means the stamps are built to be flexible around their edges - mostly plains. Effectively, a Small stamp is a Cube of plains, with various terrains filling up the inside. This is also why you'll get random maps that are mostly Square around its edges - because the stamps making up the map are.
Very rarely some players reported during beta that they had started on maps that were divided into islands. This was a result of bad stamp design that didn't quite reach the edges of other stamps.
Players also reported that there were "floating waterfalls". This occurred when two stamps merged at their borders, and one border was no longer a cliff but a plains tile. Imagine a river that floats to the very edge of a stamp and then into water. If that stamp gets rotated and placed in-game, it may end up in a position where there isn't any water.
Another thing you'll notice when playing with existing stamps is they have no Cliffs whatsoever around the edges. In the entirety of all the Stamps in the game, there isn't a single Cliff tile placed near an edge. Cliff tiles are Plains tiles that get automatically converted into Cliffs for being the border between an Ocean tile and a Plains tile. This is something you'll need to be acutely aware of when making your own stamps, because the Cartographer will turn those particular tiles into Cliff tiles by default. But under no circumstance should your Stamp contain any Cliffs around its edges. This will lead to severe distortions in-game when your tile does get placed (because Cliff tiles are NOT returned to Plains tiles when they border two Plains tiles). Placing Cliffs in the belly of a Stamp is fine however.
Making my own Stamps
Forging my stamps
If you skipped down to this part, go back up and read "Stamps Merge".
The easiest way to create a new Stamp is to go into the Cartographer, place an existing Stamp and edit that one. This will give you a stamp that is the "right" size for the sectors of a random map. Make sure that the stamp is not connected to any other stamp in the cartographer, or you'll have troubles selecting it when its time to export it.
I won't go into detail here about how to use the Terrain tools and stuff like that. Just play around with it and you'll get the feel for it.
When finished with the terrain,use the Selection Wand, click on a Plains tile and your Stamp should be automatically selected: http://i.imgur.com/haaCI.jpg
Note: The Cartographer has a bad bug that prevents you from generating a map (empty or not) then generating a new one. When you are on your second map, you will be unable to see or place Starting Positions, and you'll have difficulties selecting stamps using the wand. I strongly advise that you re-start the game after you fill the first map up.
Note: It is STRONGLY advised that each Stamp has at least 1 Starting Position with at least 4 possible tiles to settle in. Keep in mind that those tiles may well contain Monster Lairs or World Resources or Quests that prevent you from settling there. Unless you are careful, you may inadvertently create a starting position that the player cannot settle in. In order for a tile to be settlable, it must fulfil certain conditions that are too numerous to tell here, but SPECIFICALLY, one tile must be Plains or Forest, and it must be surrounded by 8 other tlies that are also Plains, Forest or River (no more than 4 forest!). ALL those tiles must also be either Kingdom or Empire environment (use Environment tool). That means that in order to create 4 suitable locations, you must cover an area that is at the very least 12 tiles large. Pay special attention to the Starting Position tile, because that is the one tile that is guaranteed not to contain Monster lairs or World Resources.
Note: Keep in mind your stamp may be rotated in any direction (north, east, south, west). Take this into account when planning your stamp. It must connect at all 4 corners to be sure that the Stamp will not create islands. Also consider how the stamp is laid out if it ends up in the very corner of a map.
If your stamp has Cliffs in it at the edges (remember, it shouldn't!), I suggest you go into the XML of the Stamp (\Documents\My Games\FallenEnchantress\Stamps) and search for Cliffs and then replace them all with "Land". Keep in mind, cliffs in the belly of your stamp can be safely turned into Land because they'll be turned back into Cliffs when the stamp is placed.
Examples of bad Stamps
Examples were replaced in 1.02 with new stamps, they are no longer broken but I keep them here as a demonstration of poor stamps.
Consider the following stamp: http://i.imgur.com/e783M.jpg. It is the infamous S_Generic_Medium_08 stamp (green borders). Notice the starting position in the top left. A very small starting position with only one direction to expand. There are Hills and Forests and Swamps that will slow the expansion down. To top it all off, once that player gets off the "long dong of doom", there is actually a starting position placed there which means there may be another AI placed there on what is the first natural expansion. And to make matters EVEN WORSE, the distance from the top-left starting position to the top-right small isle is perfect for the game to place top-level monsters there, such as Dragons and Umberdroths. If you start in that top-left position on this map, I suggest you kill yourself because you are going to lose. Even if the stamp isn't rotated horribly, is it still a fun stamp to have in a game? Potentially taking up ~40% of a tiny map? I don't think so.
Here is another stamp with a terrible start: http://i.imgur.com/RRNWS.jpg. The S_Generic_Medium_03 stamp offers similar problems as the one above. Over 20 tiles of Forest, Swamp, Hills. And the first natural expansion actually has another starting position, which means there's a good chance there'll be an AI there waiting.
But I think all those pale in comparison to this next stamp: http://i.imgur.com/k1lRU.jpg. The dreaded, instant-game ender S_Chasms_medium_05. The red cross is a starting position. It looks alright, doesn't it? A nice little peninsula with tile yields that will give you a decent start? WRONG. The Plains tiles around the starting positions get turned into Cliffs, which means with a nearby Champion, World Resource and Monster lair you are 95% certain to not get any settlable location at all. Making matters worse, there is a big nasty forest blocking your way off the peninsula (commonly ripe with Black Widows now).
Saving my Stamps
Once you are satisified with your stamp and have it selected like the screenshot above, Click Save Stamp and you'll be taken to this menu: http://i.imgur.com/wESWi.jpg
Make up a unique name for your stamp, then ignore all the other settings because I literally have no friggin idea what they do.
When it is saved, go into the Stamp XML (\Documents\My Games\FallenEnchantress\Stamps) and replace stuff as follow:s
<Frequency> determines how often the Stamp will appear. 0 means never (used for Wildlands and Spell stamps that are placed through other means). 4 is very high. Keep in mind there are 121 Stamps in the game so it will take a while before you see your own.
<Style> determines for what map types the Stamp will appear in. When the player creates a Random map in-game he can choose a Map Type as well. Note that these Styles are not equal to the Map Type, they are subcategories. You can find more info about the specifics in CoreMaps.xml. A balanced Tiny map, for example, will select Generic stamps, but a Tiny Swamp map will choose Stamps with Styles Swamps and Rugged. The reason I included all the Styles in the above quotes is simply so the Stamps can appear in every Map Type.
<Rules> - this is what I have no idea how to generate properly when saving from inside the Cartographer. The Rules quoted above are copied from the vanilla stamps, and I don't know exactly what they do, but I do know that those rules will result in the Stamps appearing in-game in Random maps.