Mr

Hi what is the diffrence of the MAP sensor reading at sealevel vs inland.

Depends on the elevation (and weather conditions - barometric pressure on that day). Here is a page with a table of info:

https://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

So the barometric pressure at sea level is approximately 101 kPa, but at 300m elevation, it's only 97.7 kPa. This offset may apply to your MAP reading for a normally aspirated car. Often the ECU has a separate barometric compensation, either from another sensor, or a reading of the map sensor when the engine isn't running.