Convert Real Life Speed to Unity Units

Hello! I have a program with the goal of tracking Aircraft in real time using open source data. This data contains various things but most importantly, speed data. Now, aircraft are fairly fast all things considered. If I get a speed reported of 400 MPH, I need to convert that to a speed that unity understands. Unfortunately, unity used a coordinate grid like the real world which is useful when putting the planes at coordinates but not representing speed.
As you get further from 0,0 in the real world, the smaller coordinate blocks get (mile x mile wise). So, 400 MPH from 0,1 will cover more coordinate distance than it will cover from 1,2. Is there some sort of quadratic function or other type of math equation that will be able to convert MPH to coordinate points per hour that would get smaller the further you get from 0,0?

I apologize if this is hard to understand, I can attempt to rewrite this if it makes no sense.

I have found the answer, it was much simpler than I thought. For anyone that wants the answer, just take your speed (assuming its in knots) and divide it by 216000.