Sunday, April 10, 2011

One Mapper, One Year

Today is the one year anniversary of my first OpenStreetMap edit! I thought I would take the opportunity to reflect on how OSM and myself have had an effect on each other. My intention is not to brag about all the mapping I have done but rather to point out some different ways in which contributions can be made and some of the tools I use when mapping.

My very first edit was to add a foot/bike path near my apartment so that it would show up on OpenCycleMap. Unfortunately the imported TIGER roads were so far off that I had to realign them before I could add the path in the correct location. And of course correcting the ones right around the path led me to correct the ones connecting to those and the ones connecting to those and so on... At the time I didn't even know what TIGER was or what all those tiger:* tags were on all the roads.

Some highlights since then:
  • GPS trackpoints uploaded: 283,271 in 75 traces (most from my Garmin Edge 305)
  • 410 changesets created using Potlatch, JOSM, OsmAnd and Vespucci
  • Pictures taken: over 2,000 (4.5 GB saved)  Most were geotagged to a GPS trace to aid in mapping features (uploaded some of them to
  • Some of the locations I have edited: 
  • Map objects affected (according to - last updated in January)
    • Nodes: about 165,000
    • Ways: about 24,500
    • Relations: about 500 (I created over 200 county relations in 3 states since the last update)
  • Contacted multiple government agencies in Kansas to get explicit permission to use their data to assist in mapping. Documented these data sources on the Kansas page in the wiki
  • Started a blog (self referring link!)

Now for a pretty picture. Here are all the GPS traces in my city. I think there may be one or two from other people but most of it is me.

Friday, April 8, 2011

Keeping a database up to date with osmosis

This is a follow-up to my previous post about importing a planet file into a pgsnapshot database schema. However the same basic process applies to other schemas that osmosis can write to.

To briefly set the stage: After downloading the weekly planet file and processing/importing it into a database, the data is now probably 3 or 4 days old. OpenStreetMap provides both minutely and hourly change files that can be applied to the database to bring it up to date with what is live right now in the master OSM database. If you think about it, that is actually a pretty sweet deal. Someone on the other side of the planet can spot a new restaurant while on their lunch break, use an application on their phone to upload it to OSM and you will get the change applied to your local database in less than  120 seconds. Does this blow anyone else's mind just a little? Open data is awesome like that.

Sunday, April 3, 2011

Parse the Planet! (into a pgsnapshot database)

What makes OpenStreetMap... well... Open? In a link:

Yes, of course there are the legal issues of having an open license, the transparent community processes to govern the project and a whole host of open source software to create, manipulate, consume and display map data. But at the end of the day, none of that would matter if the raw data wasn't available.

As is obvious from my previous posts, I have dabbled in manipulating this raw data in the past, with varying degrees of success. After learning from my previous attempts and hanging around on the mailing lists and IRC channel, picking up information here and there I decided to take another crack at processing a planet file. I ended up finding a partner in crime: Paul Norman. He was wanting to import a planet file for use in a private XAPI server using the new java based XAPI implementation written by Ian Dees. This sounded like a good idea so I decided to follow along. We bounced commands and results off of each other for a while. I ended up going a slightly different route in some of the processing because I had some different hardware available to me.

The first thing to know about processing planet data is that there are several different database schemas that can be used to hold the data. This topic probably deserves its own post at some point. Here is a brief list of the ones I am at least minimally familiar with. I know there are some others (like the gazetteer database used by nominatim):
  • API database: Creates a duplicate of the master OSM database. Does not use any GIS features. Nodes are stored with lat/lon values as simple numbers. Contains tables for: ways, tags, users, changesets. Can track history of objects once you start applying updates.
  • "pgsnapshot" schema: creates a schema that utilizes the GIS features of postgis that allows you to run spatial queries against OSM data. Still maintains all tag information but they are in a single "hstore" column, not in their own relational tables. Changesets are not stored nor is any information about users except the ID and username. History is not maintained as updates are applied. There is also a related "pgsimple" schema that seems to be an older version of the pgsnapshot schema that may have some advantages. Differences are discussed in the "pgsnapshot_and_pgsimple.txt" file in the osmosis script directory.
  • osm2pgsql rendering schema: This schema is created by the osm2pgsql tool and used by mapnik to render map tiles. It uses GIS features as well but it is lossy and very de-normalized. Only objects and tags that you care about rendering are imported. This means it is also smaller and faster to get set up.

The XAPI uses the pgsnapshot schema so this is what I set up. The instructions on how to get going are provided in the xapi readme file but I will go ahead and copy it here with some additional notes.