Spline for (lat, long, elevation) -> (x, y). Does something like this exist?

I'm working on a mini project which requires the mapping of 2d/3d geo-coordinates (e.g. lat - long - elevation) to 2d space (x, y).

Given a small area to work with, I'd like to select a point on my source map (lat, long, elevation) and associate it with a 2d co-ordinate on my target map (x, y). After I've done this for a number of points, I'd like to build a function which returns (x, y) given a (lat, long, elevation) which falls within a specific range.

A spline sounds like a good fit for this, however after many hours of googling, I've only found them of the form:

x_0 -> x_1
(x_0, y_0) -> z (bicubic)        

What I'm looking for is:

(lat, long, elevation) -> (x, y)

Is something like this available? Maybe spline isn't the word I'm looking for? I'm currently applying a simple linear interpolation between each point, but I'm sure there are better techniques out there.

Any pointers would be appreciated!