Cartography is required to read treasure maps and is therefore a necessary skill for the Treasure Hunter. There are 5 levels of treasure maps, each level has better and more treasure than the previous one - and more powerful guardian monsters protecting the chest!
To train your cartography you will need to make maps. To create a map, you need a mapmaker's pen (may be bought from NPC mapmakers or made by players with sufficient tinkering skill) and a blank map in your backpack. Double click the pen to open the crafting menu for cartographers.
Starting Out:
To begin you need to find yourself a mapmaker. These generally can be found in provisioner's shops, by docks in some cities, and also in Shipwright shops. Once you have found one, buy all the maps he/she has. Even the ones that are already drawn on. You see, for every map that you sell him, he will spawn a blank map, that you can draw on, in his inventory. You can actually draw over the city maps that he sells. If the mapmaker that you found has no maps for sale, then just keep looking.
Cartography is a difficulty based skill for purposes of gaining. This means that each of the 4 types of map you can make by using the skill on a shop-bought map needs a different level of skill to be successful. The two map types that are important are the local maps and the world maps. Local maps are useful because you can gain from then to around 60ish, and they can be sold back to the shopkeeper regularly. World maps are useful because they are what you need to draw to get up as high as you can by drawing maps.
After you have drawn on all of your blank maps, you have to sell them back to the mapmaker so he can recycle them into new ones. I would sell no more than 20 maps before buying them back. Or else you run the risk of 1) someone else buying them, 2) the mapmaker resetting and you losing your maps either way. The normal price to buy a blank map is 6 gold, and the average price for a local map is 7 gold. Remember you are not in this for profit, your goal is to become a GM Cartographer so you can read those high level treasure maps.
Gaining Cartography skill:
Any map you buy from a mapmaker can be used for cartography. You can over-write a mapmaker's map, but you can't over-write a player made map or a treasure map. When you are just starting out, you'll want to buy blank maps, as these are the cheapest. Buy as many as the mapmaker has. Click on your mapmaker's pen and select a map type to create. These are difficulty based so you will want to click the arrow to the right of the map types to see the skill required to make each map.
Note: No one is able to gain skill past 99.5 by making maps like this. From this point on, you must decode treasure maps to gain. It is wise to start collecting as many level 2 to 4 treasure maps as you can once you reach about 85 Cartography. Save them for when you hit 99.5. It seems best to stop decoding once you gain 0.1, saving the rest of your treasure maps for another session. Expect to need upwards of 500 treasure maps to GM the skill from 99.5. Do not bother trying to raise by using level 5 maps, they are too hard to even attempt, and you will not gain by using them.
What Happens When The Mapmaker Has Run Out of Money:
The first thing to check is to see if he has any maps for sale. If so buy them. Unless you are close to your carrying capacity, or really just don't want anymore maps.
If the mapmaker is out of money and has no maps for sale, then you can just donate money to him. This will add the money to his inventory so he can buy more maps, and you get the money back right away by selling the maps. As a bonus, you may even get some karma :-)
Read about life as a Treasure Hunter for more information.