There are a number of things that you need to be clear about to answer your question:

• There are three directions commonly referred to as "North". Magnetic North, Geodetic North and Grid North. You need to be clear which one you are using
• Presumably your starting point is a geodetic location (i.e. Lat/ Long) not a projected one (i.e. X/Y like UK National Grid or US State Plane)
• What level of precision do you need?

Here are some hints:

• Assuming a spherical earth makes calculations much simpler but less accurate
• Things get more distorted near the poles, if you are only interested in locations below the artic circle you can simplify
• Things get more distorted as distances increase, if you never want any distance more than 10km then simple geometry will probably be good enough

You can go all the way from doing a simple bit of trig (e.g. how long is 1 degree East-West, how long is 1 degree North-South and interpolate) to using a full blown coordinate conversion system. You have to decide how much error you are prepared to tolerate and how much time you want to invest.

A few months ago I looked into location conversion modules in CPAN and did not find any that met my needs.

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