Let me waste some of that precious time of mine explaining this to you:
http://prnt.sc/cr0i7eThis is an inkscape document.As you can see,it is the first thing that pops up.
Before you go about making any changes you need to make sure you measurment is set in pixels:
http://prnt.sc/c2eb6tYou can draw your map,do whatever you want,and then save it,which is something I assume you already know.