How do I download OSM maps????

Use OSM map file gmapsupp if you're loading the map directly onto your SD Card or Garmin internal memory.

Thanks Jamie,

I appreciate the response. From openstreetmap.nl I've managed to download a zip file of my state, but I'm not sure what to do with the unzipped files.
I am a noob at this so fairly confused.

You've got the zip file. And extracted it? It sounds like you have. If not, right click on the zip file and choose "Extract all." Click on yes a couple of times. You should now see a folder with the same name as the zip file, but this time it's a regular folder, and not a zip.

When you unzip that folder, you'll see another file inside. The following instructions are from here: https://help.openstreetmap.org/questions/4810/what-should-i-do-with-a-gmapsuppimg-that-i-downloaded

1. Connect your Garmin to your computer via a USB cable.
2. Put your Garmin in USB Mass Storage mode. (On an eTrex, this is typically done by going to the menu screen, then Setup -> Interface -> USB Mass Storage.)
3. The Garmin should show up as a removable disc (like a USB stick) in the usual place. On a Mac, for example, this will be on the desktop.
4. If there isn't a folder on the Garmin called 'Garmin', create one.
5. Into this folder, copy the .img file that you downloaded.
6. Rename it to gmapsupp.img if it's not already called that.
7. Eject the Garmin as you would a USB stick. Again, on a Mac, you do this by dragging it to the trash.

Alternatively, you can take the SD card out of your Garmin and plug it into your computer (if you have the microSD adapter and an SD card slot on your computer.).

If you're still having trouble, try to describe where you're getting stuck and what happens and we'll see if we can get you back on track.

Hi Stinky, as a fellow mac user, I just recently went through this process. Are you trying to import the map in to BaseCamp or a Garmin device?

Either. I've pretty much given up on Basecamp. I've made it as far as getting .img files on my Montana in the Garmin directory- some of which will open, and some won't. I have no idea why. I'm not sure if it's something I'm doing or if they are bad files. The map source I'm using is GPSFileDepot.

I'm away from my computer currently, so below is from memory.

Edit: I updated the steps now that I am back at my Mac.

For the Mac, when downloading BaseCamp; you get 3 applications.

1. Garmin BaseCamp is the application used for tracks, routes, etc.
   
2. Garmin MapInstall appears to be the application used to communicate with Garmin devices.
3. Garmin MapManager is the application is one used to import maps to be available in BaseCamp.

So, find the map you'd like to have and download it.
Open the Finder and navigate to downloads (there may be a shortcut on your computer) and click on the map file to unzip or extract the map.
Make sure Garmin BaseCamp is closed.
Open the Garmin MapManager.
Select open in finder button on the lower left.
Drag the the map file you just downloaded and unzipped from the downloads folder into the Garmin MapManager folder.
Close Garmin MapManager and open Garmin BaseCamp.
There is a "Map" option on the top menu where you can select which map you'd like to use.
That's it...

Unfortunately, I cannot help you with the Garmin device as I only use Android for navigation (smart phones/tablets).
There is a good resource for using BaseCamp on Macs at the following link: https://www.newenglandriders.org/learn-basecamp/

Thanks. I got it into Basecamp, but now cannot for the life of me get it to load onto the device. There is no option to transfer the map from Basecamp, and if I manually insert the .img file on the SD card, the device ignores it completely- while I have others on the card it reads just fine.

I use OpenMapChest.org to get my full country maps for most places. I also use http://garmin.openstreetmap.nl/ and https://extract.bbbike.org/ to download specific areas. I donated to openmapchest which allows torrent downloads but also allows for downloads of some of the larger countries file with installers for BaseCamp which is nice for creating routes for use on the same maps you'll use on your GPS. I also use GMapTool with MapTK to take image files downloaded from http://garmin.openstreetmap.nl/ and https://extract.bbbike.org/ to make BaseCamp map installers.