I’ve been occasionally looking at OpenStreetMap project for some “free/opensource” directions, location information, etc. But usually the results for the places I’ve searched were quite poor. It was making me sad and reverting to a mainstream mapping services.

And then I’ve got some free time, and decided that I should not spend the days home, and explore the world that is immediately around me instead. Pairing this with the low quality of Jamaica Plain map (where I currently am) in general, I decided to try fill in as many blank spots as possible.

Source Data

The first thing I found was the ArcGIS-based service from City Of Boston - Boston Tax Parcel Viewer. After spending an hour trying to learn more about map tile services in general I found that there is a MapServer with WMTS support. Since some of the buildings I knew were shaped quite accurately there, I decided to start using is as a common base layer.

Most of the building shapes in Boston in OSM comes from Orthoimagery paired with LIDAR data from some older days as well as people mapping the buildings from Bing imagery. There is newer data available from 2011-2015 Ortho Imagery. I may later switch to these maps even though the rooftop analysis is error-prone, but it is still much better than retracing the buildings from Bing.

The roads for Boston were imported from MassDOT using the data from 2007 and don’t seem to have been update since. Some of the streets had curves that weren’t there in the Basemap or the real world, so I got new ones dated 2013.

The first thing I noticed a long time ago is that a lot of maps in US don’t show the building numbers. Which is not much helpful when you try to figure out the location of the building you’re looking for while walking around. At some point for complex side streets it turns into bruteforcing, and having seen it is actually possible to obtain the address data from Tax Parcel service, I found that Property Assessment 2015 contains just the information that I need. I converted that data into an sqlite DB and wrote a script that puts the numbers on the buildings. It is NOT supposed to be used for fully automatic numbering, since the data in the Property Assessment table contains errors, but it is a good way to obtain reference points during the actual survey.

Survey

Paired with my Nexus 5 and OsmAnd for GPX tracks and custom maps I went to look at the conflicting buildings, gather local business information, add recreational areas and remove POIs that are no longer valid. This turned out to be harder than I imagined, since you need to go to side streets to find entrances, or look for a building number under a rock, but it is also healthier than sitting in front of a computer according to my fitness tracker. That is still needed after the data is gathered though.

Processing

I am using JOSM to update the data, and the numbering script to assign the addr:housenumbers to the buildings for the streets I’m about to survey. Most of the local businesses can be found on Yelp, but I still try to get information from their website/front door pictures. It is a great feeling to refresh the openstreetmap.org website and find the area matching the real world even though all the other services still show outdated content.

After processing the data I would then upload the modified maps to my phone (OsmAnd provides conversion tool), which makes it easier to refine the data.

Tips

I am pretty new to all this, but I already found that for a successful survey you need these things:

• GPX tracks - get a portable battery charger and make those tracks. They are not that useful in densely populated areas due to signal reflections, but you will be able to retrace your path later when you need it.
• Take pictures of corners, storefronts, and most importantly, signs. Make sure you have GPS coordinates written to the photos. I can’t count the number of times I had dozens of pictures with some important things only to find that I forgot the context and they are unusable.
• If there is something on the ground that is supposedly clearly visible for the satellite/aerial photography, add a waypoint. Trees are surprisingly well at hiding everything below them. Don’t trust the winter trees.
• Don’t hesitate to ask people around if some feature is confusing. You may get a great story out of that, or you can spark an interest in exploring the surroundings.

I used to think that the way does not matter, only the destination. This week of mapping with OSM made me to appreciate the way as well.