Surveying Brasilia with Walking Papers
Last week in Brasilia Eric and I joined efforts with Luiz Carlos from the Track Source community, Fabricio and Lima from Transparency Hackers, and John from the Sunlight Foundation to survey several neighborhoods for street names and points of interest to add to OpenStreetMap. We were in town for the Open Government Partnership meetings and wanted to showcase the power of open geo data and take advantage of being in town to catch up with local community members and do useful work. Here’s a quick first report before we start entering the collected data into OpenStreetMap.
Getting started for surveying the Cruzeiro neighborhood of Brasilia. Photo: John Wonderlich.
We prepped our surveys in Washington, DC by doing extensive satellite tracing to create good ground coverage. Before we got on the plane, we selected a series of neighborhoods by street name sparseness and accessibility and printed walking papers for them. Walking papers is a great tool from Michal Migurski offering essentially a quick way to print OpenStreetMap onto a series of papers, linking them back to OpenStreetMap with a QR code.
Underestimating the dimensions of Brasilia (it’s at least twice as large as a first look at the map would suggest), we had initially printed our walking papers too small but this was quickly fixed by printing new ones at the hotel before we got started. Next time, we’ll take a much closer look at satellite imagery before getting started in a city we don’t know.
On the ground
We had one team in a car surveying the neighborhoods, and another team walking. The car had the clear advantage in Brasilia, where traffic density is comparatively low and street blocks are large. Working with two to three people per team, we collected block name data and points of interest, entering it on our walking papers.
Aside from the walking papers, we used GPS trackers and cameras to capture points of interest and, from time to time, our assumed location on the walking paper. By synchronizing the camera’s time to the GPS tracker’s time, the photos can be geo coded and used later for reference. This saved us time jotting down long names of points of interest and gives us a way to double check the accuracy of our survey now.
Saving time by taking a picture of what otherwise needs to be jotted down. Screenshot from JOSM after geocoding.
Double checking by taking a picture of the assumed location on the map. Screenshot from JOSM after geocoding.
A special challenge was posed by the fact that Brasilia does not use street names, but rather block names. Brasilienses are quick to admit that the system is messy and indeed it was hard to wrap our minds around it. Even with the help of local Luiz Carlos, we had trouble, as the block system slightly varies in different parts of the city. In Taguatinga for instance, commercial blocks occupy a full city block, while residential blocks occupy two block halves around a street.
Taguatinga residential block sign. Q stands for Quadra (block), S for Sul (South). C is the alphabetic section letter, 9, 10, 11 are different block numbers found on this street.
We’re using JOSM for data entry. In JOSM we loaded up our GPS tracks and synchronized them with the pictures we had taken. Once the pictures are synchronized, it’s straightforward to enter data in OpenStreetMap using the information in pictures and the notes on our papers… if it wasn’t for Brasilia’s block system.
Synchronizing the GPS tracker time with camera time by simply taking a picture of the GPS time. Screenshot shows the JOSM dialog comparing the actual photo time with the time read from the GPS tracker.
Before we enter actual block name data, we need to better resolve how to capture them. Turning block names into street names (like Google and others do) forces awkward compromises where streets are shown between two differently named blocks. At the same time, OpenStreetMap does not seem to provide an appropriate tag for blocks. Existing block name data in Brasilia is entered inconsistently. I invite you to join our discussion on the mailing list to hammer out a solution.
If this has gotten you interested in surveying your own neighborhood or the next place you’re traveling to, LearnOSM - Using Walking Papers is a great guide to get started.