Yes, to the degree that a house at the pole will take up all of the top row of pixels as the scale goes to 0 or infinity depending on how you measure it. Our normal Mercator style Earth map does significantly distort the areas of countries leading to a very false sense of land mass size.

I don't know if you have to have a fixed scaling multiplier for larger scale maps especially since it also depends on the latitude, but you could specify that as a requirement if you like. If you want to make a single map of all the plots then you do need to resample all the map images together. That's normally a nightmare which is why I wrote my app.

You will find that city maps will probably need to be more than 20x resolution on the original bitmap scaling. Its likely that you will need a bitmap scale of one pixel to about 20cm so that is more like 1 pixel on the original map is 20,000 pixels of city mapping at the equator ! Or to put it another way - one pixel of the original map is not likely to cover a whole city in a normal fantasy demographic. So you wont be able to make one bitmap to hold all the world showing anything with city like detail.

You are bound to have discreet mapping levels or to use a zoom style map browser.