Maps Not Showing Up In Map Selection?

That you have subscribed to the map via the green "Subscribe" button on the map's page. Once in game, make sure you click "Mods" on the menu screen. From there enable the map and then click "Next".

If you don't know, modded maps will appear under the "Additional Maps" category after clicking on the map type button in the game setup. If they don't appear, then go to the next step for some possible fixes.

Option #2 is the simplest.

For this, I know of two options. If you have more (especially for other platfroms that are not Windows), please say so in the comments of this guide.

Go to your Documents folder (will usually be located in C:\Users\InsertYourNameHere\Documents) and find the "My Games" folder. In there will be a "Sid Meier's Civilization 5" folder, in that a "MODS" folder.

Find the folder for the mod in question and open it. You'll be greeted by two files. I am using my own mod (Terraformed Mars) as an example:

Open the "MOD.modinfo" file with any text editing software such as Notepad. You'll see something like this:

At the bottom, make a new line after the "</Files>" and insert this:

So it'll look something like this:

Now save the file and enable the mod in Civilization 5 and it should appear.

Go to your Documents folder (will usually be located in C:\Users\InsertYourNameHere\Documents) and find the "My Games" folder. In there will be a "Sid Meier's Civilization 5" folder, in that a "MODS" folder.

Find the folder for mod in question and open it. You'll be greeted by two files. I am using my own mod (Terraformed Mars) as an example:

Copy the .Civ5Map file and go back to your "Sid Meier's Civilization 5" folder. Then go to the "Maps" folder. In there, paste the .Civ5Map file. Now you don't even have to enable the mod for it to appear in the singleplayer game setup.

To prevent maps not showing up in map selection, follow these steps when uploading the map to the workshop.

In Modbuddy, before building the mod solution, right click the mod in the solution explorer and click on "Properties".

You should be presented with something like this:

Near the top Left, click on the "Content" tab.

Now, click on "Add..." and a small window called "Add Content" will open with Type, Name, Description and File spaces. Fill them out.

Click "OK" and now you can build the solution and upload the map.