Zoom and Images Query

Hello,After i got my moving map together, i have two questions1. I am having trouble to understand the Zoom variable (in XML Gauge Maps).For example I want a 500 nm zoom, according to the SDK documentation, it's calculated 500 nm x 1852 m/nm = 926000 m, however the manual says the range of values allowed is 80 to 500000 px/m, what am I missing here or does FSX assume a value somewhere :(2. Could somebody please explain resolution, scale and pixel conversion (in general images and/or map projections) from latitude and longitude to pixel coordinates or a website resource(s)?Much appreciated,Adrian