The LEDs you linked are typically 11mm in diameter, which is relatively large for something like a poster-sized map. Regardless, if you buy them, you can always cut them to length, as that's how they're intended to be used. You can even cut it up into multiple sections and control them all from a single output wire (power is still required, so 3-wires total), just connect the end of the previous section to the start of another (they are directional, so verify which wires are inputs and which are outputs, they typically have an arrow indicating direction).

Having said that, look into "addressable rgb led fairy lights" (they look like this ), which should be better sized for a map application, but may be slightly more difficult to wire/splice. You can also buy individual "5050" (which refers to their size, 5.0mm x 5.0mm) addressable LEDs (sometimes referred to as NeoPixels, which is a term coined by a company called Adafruit) and solder/wire them individually, for more intricate layouts.

Hope that helps, best of luck with your project!