OpenStreetMap

One Year of OpenStreetMap

Posted by asciiphil on 16 March 2011 in English (English)

Today is the one year anniversary of when I joined OpenStreetMap, so I figured I'd look back at some of the large-scale work I've done in Maryland.

I started out not even knowing about OpenStreetMap; I just wanted a program for my phone (a first generation Palm Pre) that would track my travels and draw pretty lines on a map. I found MapTool, which used OpenStreetMap tiles. At some point I figured out that I could edit the map it was showing and started to do so, beginning with the areas I knew well around my workplace and home.

My first large edits were to the county boundaries in Maryland. I noticed that they were in the database but weren't being rendered, which I realized was because they had no admin_level tag. Because I'm a completionist, rather than fix just the boundary that bugged me initially, I converted all the county boundaries into multipolygons with shared ways and made sure each way had an admin_level.

At some point, I found that the USGS had six inch resolution imagery for all of Maryland, even the really remote counties. That gave me the ability to "see" into places I couldn't walk into and places that were too far to visit and revisit in multiple surveying trips. In particular, the resolution was good enough to trace individual power lines through a messy substation that was very much access=no to me. I decided to try to map all the power lines in Maryland. After several months of work with the aerial imagery, I got the map to the point where every power line in Maryland (as of the 2007/2008 imagery) was mapped, and any data from the TIGER import that did not represent an existing power line was removed. (Or just reduced to a minor line. A lot of sub-100kV lines were tagged as power-line via TIGER.)

Here are the before and after renderings:

Maryland Power Lines - 2010-03-17 Maryland Power Lines - 2011-03-16

Obviously, people have been busy in other states, but every line in Maryland was my handiwork.

The next major task I completed was fixing the administrative boundaries in Maryland. The TIGER data had two problems: it was good for low zoom views of the boundaries but could be off by hundreds of meters in places, which became apparent at high zoom levels; and it didn't include the Potomac River or the Chesapeake Bay. I went through and realigned every county boundary in the state, as well as the state border. In many cases, the counties are separated by waterways; for those, I simply traced the waterways from the USGS aerial imagery and then tagged the ways as both waterways and administrative boundaries. For the rest of the boundaries, I traced from old USGS topo maps.

Here are before and after renderings for the whole state and a couple of detail sections to illustrate the inaccuracies in the TIGER data:

Maryland Boundaries - 2010-03-17 Maryland Boundaries - 2011-03-16

TIGER-Sourced Maryland Border at Warnocks Improved Maryland Border at Warnocks

TIGER-Sourced Maryland Border at Paw Paw Improved Maryland Border at Paw Paw

Note that one of the things I did as I worked on the county boundaries was to take large rivers that were imported as coastline and retag them as riverbank. The old data that I used to render the "before" images doesn't have those riverbanks, obviously, but I used the current coastline data, since there are no historical downloads for that (that I know of, at least), so the old renderings don't have those regions as coastline either.

My most recent project has been the railroads in Maryland. Like the other things, it started with a local annoyance that grew into a statewide project. As I was tracing the rails for the above-ground portion of the Baltimore Metro, I decided to take care of the railroad that they run next to. Some portions of that railroad were tagged as name="CSX Transportation", while others were tagged name="Western Maryland RR". It seemed to me that those were the names of the companies that owned the railroad, not the names of the railroads themselves. I started researching things and found that entire section of track was owned by CSX Transportation (which was formed by a merger that included a company into which the Western Maryland Railroad had previously been merged) and they called it the Hanover Subdivision. I decided to apply the same level of research to all the rest of the railroads in Maryland. I'm not quite done with that. I've aligned and tagged everything in Maryland with two exceptions: the southern portion of Harford County is missing its USGS imagery and the Bing imagery isn't quite good enough to follow railroads unless you're lucky, so I haven't cleaned up the rails in Aberdeen Proving Grounds or the apparently abandoned cluster of rails near Edgewood. The other exception is the Patapsco and Back Rivers Railroad, which operates in the old Bethlehem Steel plant at Sparrows Point. It's actually kind of fascinating that they have their own, separate railroad company, but a) there's a lot of rail there, so cleaning up TIGER is a lot of detailed work, and b) I started on it once, got about a third of the way done, and JOSM both crashed and corrupted its autosave file. I'll get back to it once the pain of losing all that work has sufficiently faded. Otherwise, I've cleaned up all the active railroads in Maryland and either deleted or retagged TIGER ways for now-disused railroads.

(I'll note that my criteria for disused versus abandoned versus deleting the ways is this: if the tracks are still mostly there, tag railway=disused; if the tracks are mostly gone (with maybe occasional short segments remaining) but the path of the railroad is still discernible (via topography or property lines, usually), tag railway=abandoned; otherwise, if there's no evidence that there was ever a railroad there (the land has been level and a housing subdivision built, for instance), just delete the way.)

Here's the before and after for Maryland railways, color-coded according to carrier (more or less; click through to the second one for the key):

Maryland Railways - 2010-03-17 Maryland Railways - 2011-03-16

I like the fact that the topography difference between central and western Maryland and the Eastern Shore is very obvious in the degree of straightness in the railroads' paths.

Comment from Zambelli Limitada on 16 March 2011 at 13:47

Congratulations Phil!

I am celebrating three year today :)

A before and after of the city where I started working here: http://goo.gl/c16VO

Regards,

Julio Costa Zambelli

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Comment from JoshD on 16 March 2011 at 13:48

Great work, and very impressive! I'm your neighbor over in Virginia, and while I haven't worked on any state wide projects yet, I have some in mind, such as checking county borders. Keep it up!

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Comment from 42429 on 16 March 2011 at 21:52

Congratulations! Your power lines in Maryland have been a good starting point for the Northeastern transmission grid!

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Comment from uilfut on 16 March 2011 at 21:55

Great job.

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Comment from richie0815 on 18 March 2011 at 07:03

Great job!
Where did you get the maps with the hill shading? They┬┤re very nice.

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Comment from ponzu on 19 March 2011 at 00:04

Nice post, great work! Keep on keeping on.

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