Munging OpenStreetMap Data

Answering an age old question

I like to map things. So finding StreetComplete recently was a treat! In essence, it "gameifies" contributing to OpenStreetMap which is a community driven, open-source map like Google Maps or Apple Maps, but useable by all for free.

An example quest from StreetComplete to contribute to OpenStreetMap

A question I've always wondered when driving is "what is the longest 40km/h school zone in NSW?".

Sample school zone conditional speed limit road sign

This could be answered by driving every road in the state taking measurements. Or, I could download NSW's OpenStreetMap data. Or... I could use Overpass Turbo (thanks to this blog post that mentioned it) which is an interface to quickly query the OpenStreetMap dataset. To find all 40km/h school zones in NSW within 1km of a school, all we need to do is feed it this:

// Limit the search area to NSW
area[name="New South Wales"];
// Grab every school in NSW
    // Get every road that has a conditional speed limit
    // where the condition string starts with "40" within
    // one kilometer of a school (to limit false positives)
// Not sure what these do, but it doesn't work without them
Every NSW 40km/h school zone segment and example

Excellent. To answer "what is the longest continuous stretch of 40km/h school zone in NSW" all we need to do is add make stat longest=max(length()); and we get our answer of 940 meters in "Young"[1] that seems to swing past a Catholic college, a high school and a primary school in quick succession. Also interesting are that there are 2977 40km/h road sections totalling 389km worth across the state.

While we're at it, I had another question. When driving on the M1, there's a section that's speed limited to 90km/h when raining and 100km/h otherwise. Are there any other instances in NSW?

Sample conditional speed limit sign (not the M1 one)

Not for 90/100 but there is a 80/100 in the Blue Mountains and 60/80 in Woy Woy! I'm sure Overpass Turbo is a dream for cartographers, urban planners and nerds alike.