The world we live on is kind of spheric while most maps are printed on a flat piece of paper or on a flat computer screen. To overcome this gap between our always spheric world and the flat paper space so called map projections have been invented.
A Map projection is a mathematical definition of how a coordinate on the globe corresponds to a point on a map. Unfortunately this transform can't be done without serious distorsions of some kind. Different map users have had different needs for their maps and therefore needed a projection that gave the least distorsions to their need. Some projections have also been invented just because they look cool. Here is a list of some often used projections:
One of the simples projections to understand and use in software
is the equidistant cylindric projection. Getting your hands on maps
in this format is almost impossible. The reason is that this
projection give you the sum of all distortions of all other
projections. For instance neither directions or dinstances will be
correct if you measure things on such a map. So why is it so
simple?
It's because along the X-axis (left to right) of the map you have
longitudes equally spaced and along the Y-axis (bottom to top) of
the map you have latitues equally spaced. So for a software to
transform between latitude/longitude into X and Y coordinates is
just a question of doing a multiplication of each value.
I have one map over sweden that shows pretty much what I talk about. Compare these two:
As you can see the left and right edges are pointing outwards while the upper and lower edges have become bent. What you can't see very good in this small image is that all longitude and latitude lines are now almost perfectly straight.
The worlds most common software for APRS use, UI-View, is one of those softwares that do not understand anything else than equidistant cylindric projection. This is a serious flaw in that software but since the original author has passed away and the sources have been destroyed we will have to live with it for the time beeing. Many of us have likely been tweaking those .inf files to try to get a better fit at least where we live. As we do that objects further away will get out of place instead.
The other strategy which I have taken is ot write a piece of software that can take a bitmap representation of a map and change it's projection into what UI-View likes. In fact, while I was at it I let it do other output formats aswell.
As with so many of my projects I have not really finished this product yet. It works for me but is not stable or user friendly enough to let anyone else use it. Another problem with presenting it here is that I have bought a digital map from the swedish map autorities (Lantmäteriet) and the license do not allow me to reproduce this material on the we without paying a large pile of money to them. Since the application is built with a wizard style it's not so easy to show any snapshots either but here are a few anyway.
