Sorry for the noob question but am I understanding correctly that you can simply buy a SD card for a 2016+ CX-5 (and Mazda3 for that matter) and it adds navigation to trim levels that may not have it?

Example:

 

If you have a SD card slot & "NAV" button, then, yes you are correct.

 

Thanks. Is the nav button on the screen or an actual button located elsewhere?

 

I asked this question of Mazda Customer Support of my wife's 2017 Sport. You must also have the color infotainment screen. Also, the SD cards are coded with the vehicle's VIN. An SD navigation card already coded for another car will not work in any other car.

 

You don't have to *buy* an SD card. You simply take out the existing SD card, put it into a slot in your desktop pc, run the Mazda Toolbox software, and it will update the NAV data automatically!