In short, you need to create a heightmap.png must be grayscale, dimensions: (multiple of 256)+1 in height and width.
Check out any exiting map on the Workshop for sample file/directory structure.
This tool is very helpful to place towns and industries on the map once you have the heightmap:
http://glatar.hu/tpf/TPFME-Lite.html

The only way I know of to create a map (not a scenario or savegame) from an existing game is to use this mod:
https://steamcommunity.com/sharedfiles/filedetails/?id=1445899052

Originally posted by SoftwareSimian:

In short, you need to create a heightmap.png must be grayscale, dimensions: (multiple of 256)+1 in height and width.
Check out any exiting map on the Workshop for sample file/directory structure.
This tool is very helpful to place towns and industries on the map once you have the heightmap:
http://glatar.hu/tpf/TPFME-Lite.html

The only way I know of to create a map (not a scenario or savegame) from an existing game is to use this mod:
https://steamcommunity.com/sharedfiles/filedetails/?id=1445899052

Very helpful info, thank you. Now the link to glatar....im not sure what to do with that...I understand the plain text and numerical parameters of it...but the "blurred map image" of what looks like a couple islands, I have no clue what that is or what to do with that! Would you know of a step by step video on youtube or the like?

Originally posted by D13RKES:

Now the link to glatar....im not sure what to do with that...I understand the plain text and numerical parameters of it...but the "blurred map image" of what looks like a couple islands, I have no clue what that is or what to do with that! Would you know of a step by step video on youtube or the like?

You need to click "import" and upload your heightmap.png which will then become the background image for you to work on. You may want to go to Map Settings and scroll down and change the Map Preview Width to something larger, like (just less than) the horizontal resolution of your screen, e.g. 1900 if you have 1920x1080 monitor, it makes it easier to see what you're working on. Then you can right-click at any point on the map and choose New Town or New Industry and keep adding them until you have the map the way you want. Double-click an existing point to edit; edit then click "x" to delete a point; left-click elsewhere on the map to escape the edit dialog. Once you're satisfied with your map layout, make sure the details like map name and your name are filled in under Map Settings, then click Export and save the map.lua in the same place as heightmap.png

where do I get the "heightmap.png"??

The two island map is a starting point. From there you can manipulate as required. You will require Photoshop or similar, you have to work in grayscale 8 Bits/Channel. You use varying degrees of white maximum height #ffffff, black hex #000000 being your base point i.e. sea/water. It will be tricky using the varying degrees of black and best done in a darker environment as a slight shift of black to not pure black i.e. getting slightly greyer is difficult to see but makes a big difference in the height of the area you editing. Use colour picker in PS to get greys etc. So in summary the top of Everest would be pure white and the sea is pure black. There is a site called I THINK transportfever.org or similar where you upload your map and place cities and industries. DONT FORGET ADD +1 to dimensions of your map and they MUST BE IN INCREMENTS OF 256 or 128 etc as stated by others. When you save map it must be a .PNG (ping) file and saved as 'heightmap' in a new folder called whatever you want. Save under steamapps/common/Transport Fever/maps. You then create a map.lua file in notepad but it must be saved as a.lua file. HOWEVER DO THIS AS MOST DO!
Personally I would browse maps in workshop, find one that closest to what you looking to create, then edit it in PS or similar. You can change the map size under image/imagesize USING PIXELS!!! as your measurement. Any changes to map becomes 'new art' and is your unique map. Then copy the map.lua file by editing in Notepad and fill in details so that it is unique to you! When saving DONT USE SAVE AS. Just use save, otherwise it will be saved as .txt file which is useless. This is how most maps are done. I have created a number of maps (not published) and its interesting but also frustrating especially getting an incline to be gentle as opposed to very steep! Good luck with that. You can do it by software but that's another story.

Originally posted by Cibaris:

you have to work in grayscale 8 Bits/Channel.
black hex #000000 being your base point i.e. sea/water... the sea is pure black.
...in a new folder called whatever you want. Save under steamapps/common/Transport Fever/maps.

1) Transport Fever is oddly picky about the heighmap.png format. It can be 8-bit or 16-bit, but must be grayscale. If using Photoshop one gotcha is to make sure the document is flattened, if you save as PNG from a non-flattened single layer, TpF won't like it.

2) Not quite -- #000000 is the lowest elevation on your map, which is set in map.lua -- normally pure black would equate to elevation 50m (you can adjust as needed) and water level is always 100m, so the lowest 50m of elevation on your heightmap allows you to control underwater elevation (depth of river/ocean).

3) If you only want to create a map for your own use and not shared then you can save it there, otherwise you will need to save it in the appropriate mod structure location
\Steam\userdata\<steamid>\446800\local\staging_area\<mapNameString>_1\maps\<descriptiveMapName>\
in the above dir goes both heightmap.png and map.lua, and two steps above that goes mod.lua
If you want to publish on the Workshop, you may wish to download an existing Workshop map and imitate the file/directory structure.