Having produced the continent-scale overview map for Kráva’s world. my next step was to produce a narrow-focus map for the region in which (most of) the story of The Curse of Steel takes place. After a fair amount of tinkering – and a remarkably timely suggestion from my wife – I’ve developed a workflow to do that.

As a reminder, here’s the overview map:

It’s important to note the projection this map is in. It’s in an equirectangular projection, with the standard parallels both on the equator. That means the scale only works along lines of latitude and longitude, and it only consistently represents degrees of arc. What you cannot do with this map is to assume that it has any kind of consistent distance scale.

That’s a problem for any local map, where I might want to conveniently measure off distances to estimate travel times, or the size of occupied territories, or some such thing. What I want to do is “zoom in” on a much smaller region, then change the map projection so that a flat map with a constant distance scale can at least approximate the real situation.

I spent a few hours on Saturday messing with Photoshop, trying to approximate the coordinate transform that would take me from an equirectangular projection to (say) a gnomonic projection. Much frustration followed, with several pages of trigonometric scratchings and a great deal of button-punching on my calculator (hooray for my reliable old Texas Instruments TI-83 Plus, which has been a standby for twenty years now).

At which point my wife, bless her, looked over my shoulder, listened to my explanation of what I was trying to do, and said, “Why are you messing with all of that? Hasn’t someone developed a tool to do it?”

At which point I (figuratively) facepalmed hard enough to give myself a concussion. Because, indeed, someone has developed a tool to do that.

Witness G.Projector, a Java-based application developed by NASA at the Goddard Institute for Space Studies (GISS), available for free to the public, which is all about making quick seamless transformations from one map projection to another.

Turns out that it’s trivial to load any map or image that’s in equirectangular projection into G.Projector, after which it will begin by showing you, by default, an orthographic projection of the same image – as if you were off at a distance and looking at the image spread across a globe:

Now, that much I already knew how to do – G.Projector has been in my toolkit for quite a while. What my wife’s suggestion drove me to do was to see whether the tool could do the rest of the job – move in on a specific region, and then change the projection to one more suited for making a flat map of a small region.

Turned out, that wasn’t all that difficult. A very few minutes of directed tinkering, and I was first able to zoom in on the region I wanted, and then change to a gnomonic projection instead:

From there, it was just a matter of saving that result as a JPEG image, then importing the JPEG into Wonderdraft as an overlay. A few hours of work later, and I had a very fine map to track Kráva’s progress on:

I took a few liberties in the translation, of course – added a few rivers and a terrain feature or two that weren’t on the continent-scale map. Hey, this is my world, I can fiddle with it if I want to. I suppose I might go back to the large-scale map and add in a few details, but that’s not going to become necessary unless – by some miracle – the novel actually finds a substantial audience.

More importantly, I now have a workflow I can use to produce useful, consistent maps for the expanding story, with just a few hours of work and no painstaking mathematics. Thanks, sweetheart!