I’m undertaking a bit of a project in Burnie, a city in the state of Tasmania in Australia, and thought that I should leave a more public note about what I’m doing and the reasoning behind it. Don’t expect anything particularly entertaining from this entry. The short version: a recent import of official suburb boundary data can be used to accurately offset aerial imagery, which can in turn be used to consistently align existing mapped items across the city.

While there are other mappers in the area, and I was most active in OSM mapping several years back, I’m responsible for a decent amount of data in the Burnie area. My process was pretty straightforward: drive to a new area, survey on foot, record GPS traces as I went. Back home I would upload the address data and anything else that needed updating and trace buildings from imagery. The best-quality imagery at the time was Bing, which was fairly average resolution and not always well-aligned, so I’d align the map to my GPS traces or publicly uploaded ones, depending on subjective recording quality. While this was in good faith, it meant that each little area I’d surveyed tended to have slightly different offsets, with no way for me to tell if any were correct. It’s minor, but many of the buildings I traced are also poorly outlined, though the older imagery probably limited how well I could do at the time.

Having resumed OSM mapping recently (after moving house - what better motivation than having a new neighbourhood to explore?) nobody had done much to improve this issue. Not surprising; it’s not the most populated area, things were good enough for routing purposes, and there was plenty that still wasn’t mapped at all. But it bothered me, and I noticed a new feature that made it much easier to resolve.

Burnie suburbs often split along fencelines and other structures visible from imagery, and Bing has improved their aerial imagery which now seems very well georectified. (Maxar imagery is slightly newer, but the local offset varies noticeably over small distances, especially if there are changes in elevation.) That means it’s easy to align the imagery to suburb boundaries, check that it matches well across the entire suburb/city (it does), and then align items to that imagery offset. Bing almost doesn’t need to be offset, to be honest.

I’ve thus been spending my time aligning roads and buildings to this offset across the city, rather than the hodge-podge of inconsistent alignments that existed thanks to my past efforts. I’m also doing the same with landuses, and unglueing and splitting them where necessary (which is “often”, again thanks to my past efforts). Because the city is now too detailed to download in a single request, I’m now attempting to get public roads consistent first and hope to go back and adjust all the other buildings & landuses and other data as necessary in a more piecemeal effort, probably with more reliance on the newer Maxar imagery. However, I’m not adjusting anything in the CBD as I mapped this to a relatively high level of detail in the recent past - it’s probably not perfectly aligned, but it is at least consistent within itself, and is much better than most of Burnie.

There is one obvious question - whether the suburb boundary data itself is trustworthy. In this case they were added as part of an Australia-wide import from official data, with documentation on the wiki at https://wiki.openstreetmap.org/wiki/Import/Catalogue/PSMA_Admin_Boundaries - some may have existed previously but were presumably checked for accuracy during the import. I don’t think there’s any need to doubt the original data, produced by a government with access to much better surveying equipment than I have. For safety I downloaded a copy of the imported data from https://github.com/FrakGart/psma-admin-bdy-2020-08 and compared in JOSM to the current boundaries, and couldn’t see any significant changes around Burnie. So the suburb boundaries (or at least identifiable shapes along them) can be considered a high-quality data source, reducing the need for GPS traces to align items visible on aerial imagery. And if I’m wrong, at least it will be easier to offset everything correctly in future.

Most of the addressing I’ve been doing recently has been straightforward - particularly if I happen to be doing it on the refuse collection day, since the council bins here have clear addresses on them.

Other days, you come across things like this:

(For the record, my undersanding is that the block starts on the ‘right’ at 36 Alexander Street, the building directly behind the sign takes up addresses 38 and 40, and the block ends at 44 on the ‘left’. But I’m not sure enough to put it on the map.)

The big goal of OpenStreetMap and the various themed projects is to provide a free & editable map of the world, or something like that, which is great (and so is the progress). But altruism isn’t the only reason I’ve found myself continuing to edit and contribute for the last 18 months or so.

Exercise

I suppose this is dependent on how and where you’re mapping. WIth the streets and major items filled out in my local area, I’ve moved on to the smaller things like addresses and sidewalks and even benches and picnic tables. That sort of stuff can’t really be done at typical driving speed, and it’s a lot more relaxing to just go for a stroll with a camera or notepad. I don’t know if it’s made a huge difference in terms of activity, but it sure beats watching TV on the couch. And it makes for good motivation - sometimes I can’t be bothered walking around the block a few times, but who knows what might be on an unseen street! Which brings me to another benefit…

Exploration & Awareness

Generally if I went somewhere in the past I wouldn’t dawdle - the journey was just time to kill until I got to the destination. Now though, even when I’m not directly mapping I’m more likely to take a different route, or see what’s down that side-street I’ve driven past hundreds of times but never actually needed to traverse, or pull over and take a look at the view instead of glancing out the car window. And though I’m still happy to let my mind wander on a good relaxing walk, I generally pay more attention to my surroundings, whether it’s an unsigned shortcut to the next street, or smaller stuff like “that’s a lovely garden” or “this would make a great photo”. Even on a larger scale, it’s a good excuse to go for a trip to a neighbouring town or park - not something particularly unusual, perhaps, but at least something I find myself doing more. And even if I get a little carried away or too far off the beaten track, it’s less of a problem, thanks to…

Knowledge

All that time looking at street signs and shop fronts in the real world, and digital maps on the computer later, has led to the expected result - I know my area a lot better than I did before. It’s just like most other skills, where if you just keep practising and spending time on it you improve, but I doubt I’d have spent nearly as much time “memorising” voluntarily otherwise. My mind’s-eye-copy is hardly perfect - I’m still terrible at most of the street names around here - but it’s handy to be able to have a pretty good idea of what I can buy where in town, or how to get from here to there in five different ways, or even just what’s over the next hill.

Oh, and knowing something I drew is on maps and websites all over the place is pretty nice too.

I’m not exactly why I did it at the time, but this day last year I saved a screenshot of my town in OSM. Today seems a good opportunity to see what difference a year has made - at least, in my little corner of the world.

Here’s the old one (2013-09-20) (full-size):

And new (2014-09-20) (full-size):

It already had most of the streets and roads, though quite a few were unnamed or broken since the redaction. It didn’t occur to me to take a screenshot at a ‘closer’ zoom, as the biggest changes might not look too impressive here - the CBD has filled out with just about every building and shop included, there’s (almost) no named ways without their names, and there’s a lot of smaller detail like footpaths, BBQ areas, bus stops and turning restrictions. Houses and addresses have also started to appear, and most of the urban area has landuse types tagged. However, not everything has changed; the north area near the football oval is mostly blank (construction there having not yet finished, or progressed enough to mark) and the seaport only has a few items marked (presumably due to it being private property and somewhat hard to explore, and in my case not knowing appropriate tags for that kind of thing).

If I look further ahead and compare it to the other map services, considering the relatively small population contributing to OSM locally, it’s really doing quite well. There’s one spot in particular I’m “proud” of - the section of Bass Highway here underwent changes several months back, with several new roads and one less intersection, but neither Google or Bing Maps have updated to match reality (though Bing at least has almost-current imagery).

So. Not bad at all. But there’s still plenty to keep me occupied for another year or more…