Unterbahn

The Geohash algorithm is a useful way to describe locations on the earth using a single string of a-z, 0-9 characters. They can be thought of as rectangular subdivisions of the Earth’s surface. Learn more here: Geohash at Wikipedia. They were invented by Gustavo Niemeyer in 2008.

It’s good to get an idea of how large a rectangle a given geohash describes, but this changes depending on your latitude. At the equator, geohashes are biggest, so you need more characters to describe an area of a given size, or a location of a given precision.

In Cartagen I’m using geohashes to report geodata by text message, so it’s very useful to know how long your geohash code will be to describe, say, the area of a building, a soccer field, or a street corner. I did a quick calculation for the equator, which is the worst-case scenario:

Dimensions of geohashes of length n:

I think this is right but if you find an error please tell me. I put it up on the Cartagen Wiki here: GeoHashes

Josh Levinger of GroundTruth and I tested our larger 8 foot balloon yesterday, and it was a huge success! We ran all the way through our spool of string, and got some great images before the light got too dim. I rectified them using Map Warper (fantastic!) and we now have a mostly continuous ’scan’ of our flight.

This means this can be a viable way to capture high-resolution geolocated imagery at low cost! I spent under $100 on the equipment – $30 for the balloon, $40 for the camera, $5 for the helium, and a few bucks for string. I bet it could be done for under $50 with a cheaper camera and perhaps trash bags instead of latex balloons. We’ll be trying that soon – I’d guess we need about 10 of these 98-gallon bags. I also turned the ISO way up for this because the light was failing, so the photos are pretty grainy. This camera doesn’t have shutter speed settings, though I’m still playing around with the CHDK settings so maybe I’ll do better next time.

I’m excited to test this in an area that really does not have good aerial imagery, like outside Lima, Peru.

See all the pictures at full resolution here: Balloon aerial photography on Flickr

See some great photos from the ground by Christina Xu on Flickr

Nice rendering, but not a new idea.

BBC NEWS | UK | Magazine | People-powered maps.

DIYcity is a fascinating effort apparently related to the Open Planning Project.

Our cities today are relics from a time before the Internet. Services and infrastructure, created and operated by the government, are centrally managed, non-participatory and closed. And while this was once the best (and only) way for cities to operate, today it leads to a system that is inefficient, increasingly expensive to maintain, and slow to change.

What is needed right now is a new type of city: a city that is like the Internet in its openness, participation, distributed nature and rapid, organic evolution – a city that is not centrally operated, but that is created, operated and improved upon by all – a DIY City.

Fantastic.

Map of the Sudbury Nickel Report, 1913

I’ve been taking very high-res imagery from a weather balloon and rectifying it, but the OpenStreetMap data isn’t detailed enough to find rectifying points… the result is a bit like this:

To add a Google layer, just run:

to_map.addLayer(googleSat,{'maxZoomLevel':22});

or drag this bookmarklet into your browser bookmarks bar, and click the bookmark when you’re on the Rectify page:

google-for-warper

The result is something like this:

Try the demo

I saw this for the first time at a film festival in New Haven, and could never find it – Matt found it yesterday. I guess he’s better at the internet than me. The film is by Chris Stenner.