Martian Cities Schematic Map

One of the many projects I started and stoped work on over the past decade was an interactive map of the Martian cities. A map that shows distances which allows a GM to estimate how long a trip will take. A zoomable map covering every city, canal, and junction connected by the full network of established canal and caravan routes, with a built-in route distance calculator that reports a real travel distance between any two locations you specify. The result is this schematic map. Feel free to bookmark it, it's the kind of thing I hope you'll want to come back to next time you're planning a route.

Why this map needed to exist in the first place

This whole thing started because of a practical problem. I needed to know how far it really was from Syrtis Major to Melas, in the Belgian-controlled Coprates region, so I could calculate how long a canal or caravan trip between them would take, for an adventure scenario.

That sounds like a five-minute question. It wasn't. I tried working it out from Conklin's Atlas of the Worlds first, and it turned out to be genuinely difficult. The large-scale published maps of Mars are perfect for getting a feel for the Space: 1889 setting, but they're not built for pulling a real mileage figure off of them. At that scale, the gap between "a few days' journey" and "a multi-week expedition" can come down to a couple of centimeters of map, measured by eye, with no reliable way to convert that gap into an actual distance. And that's before you even account for the fact that a flat map distorts distance depending on where on the globe you're looking. I kept taking rough ruler measurements that didn't agree with each other, and I couldn't tell if that was my measuring or the map itself lying to me.

The place to start was Dan Thompson's merged map, the one that stitches Mars's three separately-published face-maps into a single continuous reference (used here with his permission, and with real thanks to him for it, since none of this happens without that head start). Even with that in hand, my first approach was just holding a ruler up to a printed copy. That led to the idea of overlaying a coordinate grid instead of eyeballing it. That led to realizing Photoshop would handle the grid better than graph paper would. And that led to the actual idea behind this whole tool: record real X/Y coordinates for every city and canal, and use them to build something closer to a subway map, one that could report a real distance between any two points instead of just showing a pretty picture of the terrain.

So this map and its Route Distance Calculator exist to answer that kind of question properly. Name two locations and get back a real, trustworthy distance, grounded in actual spherical geometry instead of a guess pulled off a fold in a poster map. Syrtis Major to Belgian Coprates, without traveling through Oenotrian territory, was the very first route it was ever asked to solve. Of course, the players decided to take a "shortcut" through the desert, off the established canal and caravan routes, and this map handled that too (although not necessarily the encounters they'd find along that uncharted route).

Here's how it actually pulls that off.

Every flat map of a round world tells a small lie

You can't peel an orange and lay the peel flat on a table without it tearing, stretching, or bunching up somewhere. The same is true of any map of a planet. There's no way to flatten a curved surface without distorting something: distance, area, shape, or direction. Every map projection ever made picks which one to sacrifice.

This Mars map uses a projection called Mercator, the same style Gerardus Mercator invented in 1569 for European sailors. Mercator's genius was realizing that if you're steering a ship, the one thing you can't afford to distort is direction. A straight line on the map needs to match a constant compass heading in real life. To pull that off, Mercator projections sacrifice distance instead. They stretch the map more and more as you move away from the equator, so regions near the poles end up looking much bigger on the page than they really are. It's the reason Greenland looks the size of Africa on old classroom wall maps, when in reality Africa is about 14 times larger.

The distortion is exact, not random

Here's the part that matters for our purposes. Mercator's stretching isn't a fudge or an approximation. It follows a precise mathematical rule tied directly to latitude. That means the distortion can be measured exactly at any point on the map, and if you can measure a distortion exactly, you can undo it exactly.

That's what happens behind the scenes here. Every city's X/Y position on the flat map corresponds to one specific true latitude and longitude on the Martian globe, the same kind of coordinates you'd use to pinpoint a city on Earth. When the map calculates a distance, it doesn't just measure a ruler-straight line between two dots on your screen. It first translates both points back into their real latitude and longitude, then calculates the distance the way navigators and airline route-planners have for centuries: as a great-circle distance, the shortest path between two points measured along the curve of the sphere, not across a flat page.

A simple way to picture it: imagine Mars as an actual globe sitting on your desk, and you stretch a piece of string taut between two pinholes marking two cities. The string wants to lie along the globe's curve, not cut straight through the inside of the planet. That string's length is what our calculator is measuring, not the distance between the two dots as they happen to appear on your flat screen. Two cities that look widely separated on the flat map, especially near the poles, can turn out to be considerably closer together in real terms than that flat-map gap suggests.

Why this actually matters, with real numbers

This isn't a minor technicality. If you simply measured distances with a ruler on the flat, uncorrected map, you'd overestimate the true distance by about 14% on average. For city pairs at high latitudes, where Mercator's stretching is most severe, the flat-map measurement can run as much as 62% longer than the real spherical distance.

Take Dioscuria and Aryn, two real cities connected by an established caravan route. Dioscuria sits well north of the equator. Aryn sits almost right on it. Measure the gap between them on the flat map using a single uniform scale, and you'd call it about 1,939 miles. The actual spherical distance is 1,732 miles, so the flat reading overstates the trip by 12%. Nothing about the caravan route itself changed. The correction is purely in how the two points' positions get translated back into real latitude and longitude before the distance is measured along the globe rather than across the page.

The effect shows up just as clearly in a tight cluster of cities as it does over a long haul. The Boreosytris League (Meroe, Coloe, Umbra, and Saardaar) sits far enough north that the four cities are more tightly packed in reality than the map lets on. Add up the four established canal legs connecting them (Coloe to Meroe, Meroe to Umbra, Umbra to Saardaar, Saardaar to Coloe), and the true spherical distance comes to about 327 miles total. Read those same four legs off the flat map with a uniform scale, and you'd get roughly 498 miles. Every leg is overstated by 49 to 56%, because all four cities sit at nearly the same high latitude and get stretched by almost exactly the same amount. The League is a noticeably more compact, easy-to-defend cluster of cities than a glance at the map might suggest.

The upshot

Every mile shown on this map, whether you're reading a single route's length or adding up a multi-leg caravan journey in the Route Distance Calculator, is a real, spherically-corrected distance, calibrated against Mars's actual equatorial circumference. The flat map is just the display. The geography underneath it gets treated as the sphere it actually is.

Some notes about the map itself. I have attempted to eliminate any of the anomalies introduced in the original Conklin's maps. In particular, a few cities have different names on different faces (so I have chosen one name for consistency) and where one face showed a canal or caravan route that was missing on a connecting face, I opted to be inclusive. Finally, I made the assumption that the ruins indicated on the Conklin's maps were located along the paths of the ancient canals, rather than out in the Martian deserts. If you find something that I may have missed, please feel free to drop me a niote or leave a comment here and I'll do my best to rectify the map.

Happy gaming!

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