A few weeks ago I was discussing the progress of mapping the UK at one of the London OSM pub meetups (Harry picked up on it in his diary entry for the evening). I was making the point that we’re making great progress, and if things continue as they are then most towns and villages will be mapped in 12 months time. Now we’ve certainly heard that before (Steve Coast was targetting summer 2008 if I recall) but my guesstimates are based on weekly road length analysis that I’ve seen and I’m currently working on making public.

But leaving things to take their due course is the easy way out, and I think we can do most of the remaining work this summer if we collectively put our minds to it. What would that involve? Well, a few dozen mapping parties would be a good start, since there are only currently two scheduled (Witham and Maidstone). CloudMade had been sponsoring a few mapping parties in the past, but that seems to have fizzled out, so it’s up to the community to sort things out ourselves. A good source of ideas for places is the UK Mapping Priorities and Secondary Priorities pages. I’ve been updating the former over the last week, and it’s impressive how many places have been mapped over the last six months. But there are some glaring problem areas – anyone want to organise a Darlington party?

What else beyond parties? Publicity is something we’ve been reasonably poor at over the years. Getting in the press is a good way to “prime the pump” for gaining new members, and probably encouraging people who might have looked before to look again. We can just make random “press releases” about all kinds of things we do – that’s what everyone else does! I’ve just gone looking on the wiki for previous press releases, and they are woefully lacking. Whilst it’s great to get coverage in the national press, I think we should be aiming for all the local papers that struggle to find anything interesting to print. Of course, if we had those two dozen mapping parties they would be a good excuse for releases. But beyond that, lots and lots of blogging, discussing on forums and things like that. Just try to find ways to put the word out. I’m selling promotional stickers in the OpenCycleMap shop – any more ideas like that? We could get some funding or fundraising for more leaflets to hand out, or for organising stalls at trade shows, or for buying another banner, or buying our own aerial imagery.

And when we have all these new people, we’ll have more awesome tools for them. Grant is sorting out the wiki onto new, faster hardware, and I’ve been finding time to work on Potlatch2. More development helps, so if you’re that way inclined I’d love to have you helping. But it’s completely plausible to finish the UK road network this summer if we get organised and get motivated. Who’s up for the challenge?

A few months ago NASA caused a stir by releasing a new global height dataset called ASTER. I use an earlier dataset (SRTM) for OpenCycleMap, which has a few problems that ASTER, at least initially, promised to solve. The three of primary interest to me are:

• Voids – SRTM has “no data” gaps in certain places of the world, where the radar reflections went haywire. These happen in marshes (not of interest) and mountains (of great interest!), especially over the Alps. ASTER is void-filled already, so the clever-but-inaccurate void-filling I use wouldn’t be necessary
• Resolution – It’s great that SRTM covers the whole world, but I’d love to see it at a higher resolution. ASTER’s nominal resolution is three times greater than SRTM, so it’s very attractive.
• Arctic coverage – SRTM only goes as far north as 60°N, which is a bit of a problem in Scandanavia. Although there’s GTOPO30 data for these areas, that’s got a horizontal resolution measured in kilometres, so not exactly great for me. ASTER covers those areas too, up to 83°N.

So far so good. But when I started work with ASTER in December, things spiralled rapidly downhill. First is the pointlessly irritating “order a dataset” website, that sucked up hours of going round in circles. It’s like a shopping website from 1999. You need to use a stupid interface to order which 1°x1° tiles you want, and “All” isn’t an option, despite there being 22,600 of them. It seems geared up for people who want a couple of dozen at a time, and the whole thing has a feel of being run by men with beards and sandals who’d rather you didn’t use their website in anything newer than Netscape 4 on HP-UX.

When I read the README alarm bells started ringing. There’s a section on “mole runs” and “pit artefacts” that sounded a bit worrying, but I wasn’t sure how much of an issue they’d be – if they were small and few and far between then that’s not much of a problem. But the biggest thing that caught my eye, buried on page six after pages of confirmation of how good the accuracy was, right at the end of a section as a throwaway comment, was the following statement:

Also, while the elevation postings in the ASTER GDEM are at 1 arc-second, or approximately 30 m, the detail of topographic expression resolvable in the ASTER GDEM appears to be between 100 m and 120 m.

That’s a bit of a bomb-shell – it’s saying that although it’s got a much higher nominal resolution than SRTM, it’s effective resolution is about the same – there’s not any more actual detail, just more pixels. That was almost enough to make me give up there and then, but it’s still void filled and covering more area of the planet, which would be good improvements. So I grabbed the DEM (thankfully, they’re straightforward GeoTIFFs) and got to work over Snowdon. I did some colouring and contours, and they both looked excellent and much better than what I made from SRTM. But then I tried hill-shading, and disaster!

Here’s the area around Snowdon (click through for original size):

and a detail of Snowdon itself:

The mole runs are everywhere – all across that image, even on the flat bits. And the pit artefacts are huge – the size of quarries, and really, really obvious. I honestly can’t use that – maybe for a “what the world would look like if it looked like the moon” project, but nothing more serious than that. And considering that SRTM has only a handful of single-pixel voids in that area, the guys making ASTER have made something that’s substantially worse than an oversampled SRTM. And considering they were even using SRTM to fill the gaps in the ASTER data, that’s a pretty poor show. I started reading around and found a few people saying similar things. And when I though about it, the “improvements” to the contours I saw could be recreated with SRTM by using gdalwarp to artificially increase the resolution (with some nice smoothing) before generating the contour lines. So I gain nothing from ASTER in the 95% of the planet that doesn’t have significant voids, and in that same 95% it’s not really usuable.

So for now, I’ve given up with ASTER. I might revisit it for the band between 60°N and 83°N, but it also says in the readme they have voids over eurasia for that area (so much for void-filled, eh?). And it would be interesting to see if someone can fill the large SRTM voids with ASTER (which sounds back to front, hey-ho), but I don’t have time for that. However, as they say in the docs, all these artefacts are happening in the boundaries where they have different numbers of original samples, so maybe a future version will have these automatically smoothed out, and it they can figure out how to stop their 15m sampling getting turned into 120m effective resolution, that would be awesome. But for now I would say it’s not worth using it.

It was over 18 months ago that I was originally trying to get hill-shading and hill-colouring working on OpenCycleMap (in fact, it wasn’t even called that back then, but that’s a different story). I eventually dropped the hill-shading part of it due to nasty boundary artefacts between source tiles, and due to the fact that the shading, well, didn’t look as nice as I wanted. It was all a bit grey and manky.

So instead I launched just the hill-colouring in August 2008, which I was very happy with, and put hill-shading on the back burner. Time passed. Much time.

A few weeks ago, I rolled up my sleeves and got stuck in to figuring out how to do the hillshading properly. With some pointers from Matt, Mike and the OSM Wiki, I played around for a few days until I liked the end result.

Here’s a look at Snowdon before hill-shading. The colours do a good job of showing the lie of the land, but it’s a bit flat:

Detail:

And what Snowdon looks like now. The shading lifts the peaks out from the map, and gives them a more solid-object feel:

Detail:

It really helps most in complex mountains, like here in the Alps, where the contours would otherwise become a jumble and it’s hard to tell valleys from ridges. With the shading, it’s easy.

It’s a hard balancing act, since OpenCycleMap is first and foremost a map for cyclists, and too much hill-shading overpowers and distracts from the rest of the map. But then again, too little and it doesn’t seem worth the effort! I went for a subtle approach, where it’s enough to make the hills stand out but little enough you might not consciously notice. Unfortunately the effect is diminished in forested areas, and by dense contours, since it’s only the background height colouring that is shaded and those things start obscuring stuff.

Also, I was never really happy with the “drab grey” approach to shading – just making the shadows grey and the highlights white using alpha-blending – so I settled in the end for “hardlight” compositing. It’s a bit like the evolution of GUI buttons from Windows 3.11 (”right, top and left edges are white, other two edges are black, grey in the middle”) with those from MacOSX (”ooh, shiny”). Compare OpenCycleMap to Google Terrain and other hill-shaded maps, and I’m quite proud of the results.

If you have a map project that could do with some good-looking terrain info, then I’m available for freelance work.

Over the last few months I’ve been involved in three different aerial imagery projects, all of which were to make imagery available for OpenStreetMap contributors. It’s nice that we have imagery available from the guys at Yahoo!, but on occasion we lay our hands on some better stuff.

First off was Stratford-upon-Avon, here in the UK. As an experiment we hired a small plane, put one of our contributors on board with his SLR, and flew around town. All the photos were then put on line, and even though I’d never been to the place before I could use Tim Water’s online map rectifier and re-purpose it slightly to warp the photos and line them up to the map data. Other people did the same, and then I collected all the separate images and processed them into one map layer. A few days later I was at a “Traditional GIS” conference in Stratford, and there was a great deal of interest from people in the aerial imagery project and OSM in general. I can recommend it as a publicity stunt for other conferences!

You can see more pictures of the end results on flickr, or read more about it on the OpenStreetMap wiki.

Next up was the Philippines. After massive deadly flooding aid agencies on the ground were using OpenStreetMap to help with the disaster relief. Manning Sambale from the OSM Philippines community received a donation of satellite imagery of part of the affected area, and asked for help processing it and making it available. I made some space available for him to upload it, and then processed it into the right format for OSM editors. With such high-quality imagery available so soon after the disaster, OSM volunteers both in-country and working remotely set about mapping the villages and marking on the locations of bridges and damaged areas. You can get a sense of scale of the damage from the image below – the gravel banks covered fields and villages around the river, and the imagery was a huge help.

The third project was in Georgia, USA, where I got hold of some fairly recent (2007) imagery from the Department of Agriculture National Aerial Imagery Program (NAIP). Although Yahoo! has good quality imagery available across the whole of the USA, this public-domain imagery was more up to date and slightly higher quality that what Yahoo! has in rural areas of Georgia. This is by far the biggest set of imagery I’ve had access to – hundreds of gigabytes of the stuff – and only a handful of counties were processed.

I’m sure as time goes on we’ll get more and more sources of imagery to help with OSM, and I look forward to lots of “crowd sourcing” experiments like the stuff from Stratford as much as I like the imagery from the professionals.

If you have access to any sources of imagery and need a hand getting it processed, get in touch!

I wonder whether everyone missed the donations link last time, so I’ll put it first instead! Go on, drop a pound in the collections tin.

When Jon Burgess found out that I was editing the 2008 videos, he dug out his recordings of the first SOTM conference and sent me a disk full of them. This time I knew what I was doing a bit more, and the quality is much improved – in fact, if you have the bandwidth and computer for it, you can also watch them in full HD glory.

Unfortunately Jon didn’t have enough space to record all the talks, but we have 15 available on vimeo. For a full list of talks and links see the OpenStreetMap wiki, or just have a look at my video account and watch them all!

My pick of the bunch are:

• Steve Coast: “This Mapping Stuff Could Really Take Off”
• Richard Fairhurst: “Why Mashpus suck (and cartography matters)”
• Etienne Cherldu: “OSM and the Art of Bicycle Maintenance”

It’s great watching these videos – I wasn’t even “into” OSM enough back then to go the conference! And it’s nice to see the things that are wildly different now, and all the things that are still familiar topics.

Imagine, if you will, a small town with a surprisingly active pottery club. Every week they gather in the local arts centre, and spend long evenings making pottery together. They take lumps of clay and sculpt them into vases, mugs, bowls, teapots and all kinds of things. They share tips and tricks, and help each other out – some people just do their own thing, but there’s a real sense of community. It’s not surprising to find them taking a break together in the local pub, where they spend a lot of time talking about their hobby. The pottery they produce is really high-quality stuff too – a labour purely of love and fascination, not driven by cost/benefit ratios, deadlines or schedules.

Now these people are so interested in their pottery hobby that they happily make far more of it than they need, and so they give away much of the end results – after all, it’s a hobby and they have already got all the teapots they need (and maybe they have a bottomless pit of clay nearby or something that makes this analogy more plausible). And other people appreciate all the free pottery, and wonder what they can do to help. These outsiders come with fairly pure intent – they want everyone in the whole world to benefit from these high quality teapots and vases.

And so the outsiders think about how they can improve this pottery club. They come up with the idea of helping by shipping in partly-made vases and teapots, and letting the club just “finish them off”. After all, it’ll save time and be easier for everyone involved, and gets everyone towards having those next 10,000 vases that much quicker than just waiting for the club to do so in their own time and expand at their own rate. So truckloads of distorted, broken, low-quality, half-finished wet pottery starts arriving at the back door to the club. Some people start taking this pottery and trying to fix it, and a few people in the club think that it’s a great idea. But a lot of people start getting disillusioned. They realise that fixing other people’s mess just isn’t as fun as starting from scratch and making a proper job of it themselves. The banter in the club stops, and it turns into a factory line – no sooner are they finished fixing up one batch of bodged-up pottery than another arrives. More outsiders are scouting around for sources of low quality pottery – after all, if you give it to this Club then they will fix it. But the output quality starts falling as “good enough” pottery is given away, where before they would have bandied together to keep their high standards. People start enjoying the whole thing less, they start drifting away, and the club slowly falls apart. Takings also fall at the pub.

Enough of the story telling. This article is in the “OpenStreetMap” category because I want people to think of this parable when they are considering bulk imports. The strength of OSM is the community. The creation of this dedicated community is a high-quality map. There are ways to help the community, and there is usefulness in using other data sources to assist. But if we continue down the path of treating the community as a mechanism to “fix-up” broken or low-quality data imports, whether that be TIGER, GNIS, NaPTAN or any of the others, then we’ll ruin ourselves in doing so.