I have attempted to map some GPS coordinates (longitude / latitude pairs) onto an image of the region of the world that they correspond to. The math was not complicated simply offsetting and then transforming the numbers with a multiplier. However this worked fine for points in Australia, but not for points in New Zealand.
The result is that the points seem to drift south near the middle of the image then slowly correct before the bottom.
Is there some extra math which needs to be taken into consideration for plotting points on a map?
Note:
during my diagnostic excercise I placed my map over google maps and noticed that my version of Australia was different to google maps, but New Zealand was the same as google maps. But the plotting for Australia works but for New Zealand does not.
Longitude/Lattitude is spherical coordinatesystem and will only work if you have a globe to show your map on. In your case you have a flat map and need to project the coordinates onto a flat surface. The maps that Google uses is created with an Mercator-like projection.
What kind of projection you want to use depends on how big area your map consist of. Most countries have their own projection that fit best for their purposes.
Those transformations are quite tricky to work out by hand if your not a mathematician but there are good libraries for transformations like Dotspatial and GDal.