Vegetating the state with DEPI
The states' government data portals contain all kinds of data goodies that are pretty useful, if you know it's there and how to get it. Here's one: the Department of Enivornment Primary Industries' "Vicmap Vegetation 1:25,000" dataset.
What is it? A detailed geospatial data file showing areas that have trees, across the whole state.
Why is it useful for me? I run http://cycletour.org, a map-based planning tool for cycle tours. It's nice to know which areas are forested, as they're often nicer than farmland, and better for stealth camping.
Searching for "trees" on http://data.vic.gov.au turns up lots of stuff, like this:
There's a lot of technical knowledge assumed here. See the text in blue?
WMS: This actually isn't a data file you can download. It actually means the first two "datasets" are just locations of a Web Map Service - an older way of serving map tiles over the web. So it's a URL that you could give to a GIS program to change your basemap, but you're stuck with however DEPI chose to render this vegetation layer. And you can't do any actual analysis with the data - it's just a set of images.
SHP: This is a downloadable Shapefile, a very widely supported proprietary geospatial format.
And the 1:25,000? Government departments still seem to be dominated by the idea of printing maps, where scales are expressed as ratios. A dataset described as 1:25,000 means that the data is precise enough to be printed on a map at that scale. In this case, that's good enough for a pretty detailed hiking map, for instance. (The datasets also include more detailed statements like "For topographic base derived data this represents an error of 8.3m on the ground for 1:25,000 data")
Ok, let's download it.
Not so fast.
Data.vic.gov.au doesn't actually contain downloadable geospatial files from DEPI. Instead, after entering your email address, you get redirected to the Spatial Datamart, a somewhat clunky geospatial data portal. Here's what you have to do to get all the data for Victoria:
1.Choose area type "Whole of State"
2.Click "VIC", then ">". (So now it knows which whole of state...)
3. Click Apply and Submit.
You could choose a different projection, but since it doesn't offer anything useful, like, oh, the world's most popular web mapping projection, Spherical Mercator (EPSG 3857), there's not much point.
4. Sit back and wait. You'll get an email in an hour or so, letting you download the file. This one's about 1.5GB.
Then, you can do what you want with it. In my case, styling the data with TileMill, and adding a new vegetation layer to cycletour.org:
