How Much of My Graticule is Covered With Water?

I’m a moderately-keen geohasher, as you might be aware if you follow my geohashing logs or you saw that video of me going ‘hashing earlier this month.

For those that don’t know, the skinny version is this: in May 2008 an XKCD comic was published proposing (or at least joking about) a new game with a name reminiscient of geocaching. To play the game, participants use a mathematical hashing function on the current date and the most recent Dow Jones Industrial Average opening value to generate sets of random coordinates around the globe and then try to find their way to them, hopefully experiencing adventures along the way. The nature of stock markets and hashing functions means that the coordinates for any given day are effectively random and impossible to predict (far) in advance, so it’s sometimes described as a spontaneous adventure generator.

XKCD comic #426, "Geohashing"
The XKCD comic that started it all.

Recently, I found myself wondering about how much of a disadvantage players are at if they live in very “wet” graticules. Residents of the Channel Islands graticule (49 -2), for example, are confined to two land masses surrounded entirely by water. And while it’s true that water hashpoints can be visited if you’re determined enough, it’s still got to be considered to be playing at a disadvantage compared to those of us lucky ones in landlocked graticules like mine (51 -1).

And because I’m me and so can’t comfortably leave a question unanswered, I wrote a program to try to answer it! It’s among the hackiest, dirtiest software solutions I’ve ever written, so if it works for you then it’s a flipping miracle. What it does is:

  1. Determines which OpenStreetMap tiles (the image files served to your browser when you use OpenStreetMap) cover the graticule in question, and downloads them.
  2. Extracts information about the colour of each pixel in each tile.
  3. Counts the proportion of “water blue” pixels to other pixels (this isn’t perfect, because it trips over things like ferry lines on the map as being “not water”, especially at low zoom-levels).
Extreme zoom-in on Worcester College Lake, on OpenStreetMap.
Some parts of Worcester College Lake are identified as “not water” on account of the text overlay.

I mentioned it was hacky, right?

You can try it for yourself, if you’d like. You’ll need NodeJS, wget, wc, and ImageMagick – all pretty standard or easy-to-get things on a typical Linux box. Run with node geohash-pcwater.js 51 -1, where 51 -1 is the identifier for the graticule you’re interested in. And in case you’re interested – the Swindon graticule (where I live) is about 0.68% water, but the Channel Islands graticule is closer to 93.13% water. That’s no small disadvantage: sorry, Channel Islands geohashers!

Update 2018-08-22: discovered some prior art that takes a somewhat-similar approach.

Maps Showing California as an Island – The Public Domain Review

This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

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If California were a country its economy would be the fifth largest in the world (just ahead of the UK). Yet the tech boom is not the starkest way California has ever stood apart from its neighbours. That would surely be the maps depicting it as an island, entire of itself. Below we have featured our pick of these glorious seventeenth- and eighteenth-century aberrations, from a collection of hundreds held at Stanford.

The intriguing story of how the maps came to be deserves a little mapping itself. In the 1530s Spanish explorers led by Hernán Cortés encountered the strip of land we now know as the Baja Peninsula. They mistook it for an island and called it California.

Roadspotters

Recently, I learned that the roads in Great Britain are numbered in accordance with a scheme first imagined about ninety years ago, and, as it evolved, these road numbers were grouped into radial zones around London (except for Scotland, whose road numbering only joined the scheme later). I’d often noticed the “clusters” of similarly-numbered roads (living in Aberystwyth, you soon notice that all the A and B roads start with a 4, and I soon noticed that the very same A44 that starts in Aberystwyth seems to have followed me to my home here in Oxford).

Road Numbering Zones of the United Kingdom

Who’d have thought that there was such a plan to it. If you’re aware of any of the many roads which are in the “wrong” zone, you’d be forgiven for not seeing the pattern earlier, though. However, seeing all of this attempt at adding order to what was a chaotic system for the long period between the Romans leaving and the mid-20th century makes me wonder one thing: are there “roadspotters”?

There exist trainspotters, who pursue the more-than-a-little-bit-nerdy hobby of traveling around and looking at different locomotives, marking down their numbers in notepads and crossing them off in reference books. Does the same phenomena exist within road networks?

It turns out that it does; or some close approximation of it does, anyway. One gentleman, for example, writes about “recovering” road signs formerly of the A6144(M), which – until 2006 – was the UK’s only single-carriageway motorway. A site calling itself The Motorway Archive has a thoroughly-researched article on the construction history of the M74/A74(M) from Glasgow to Carlisle. Another website – and one that I’m embarrassed to admit that I’d visited on a number of previous occasions – reviews every motorway service area in Britain. And, perhaps geekiest of all, the Society for All British and Irish Road Enthusiasts (SABRE) maintains a club, meetups, and a thoroughly-researched wiki of everything you never wanted to know about the roads of the British Isles.

From what started as a quick question about British road numbering, I find myself learning about a hobby that’s perhaps even geekier than trainspotting. Thanks, Internet.