Saturday 20 October 2012

Mapping New Zealand: Clustering DOC Huts with Leaflet

In New Zealand, long distance walking or hiking for at least one overnight stay is known as tramping. There is a great network of over 950 huts throughout New Zealand operated by the Department of Conservation (DOC). I’ve just stayed in four of the huts while tramping the Abel Tasman Coast Track, and you need a lifetime to reach them all. It’s much quicker to map them.

DOC huts in the Abel Tasman National Park.

Awaroa Hut
I was fortunate to visit the geospatial unit at the DOC office in Wellington. They have a lot of ineresting conservation projects going on, and it seemed to be a great place to work in New Zealand, especially when you can combine digital work with practical field work.

You can download DOC's geospatial data for free on their data portal. Unfortunately, the datasets are not available as shapefiles, so it might require some wizardry to extract the data from KML. Luckily, the Koordinates guys have done this already, and you can download the shapefile from their website. The version I’m using was updated 10 September 2012.

The dataset contains 967 huts, and adding them all to my Leaflet map will make it too cluttered to be useful. Instead, I wanted to try the great animated marker clustering plugin, created by Dave Leaver here in New Zealand.

I start off by converting the shapefile to GeoJSON with ogr2ogr:

ogr2ogr -t_srs EPSG:4326 -f "GeoJSON" -lco COORDINATE_PRECISION=4 nz-doc-huts.json doc-huts.shp

I could use the GeoJSON directly, but I converted it to a more compact format to save some bandwith:

var data = [
  [-43.3767,170.5685,"Scone Hut",1],
  [-42.9494,171.7047,"Sudden Valley Biv",0],
  [-41.5237,172.5604,"Granity Pass Hut",1],
  [-44.9261,168.2144,"Steele Creek Hut",0],
  [-44.6221,168.4481,"Earnslaw Hut",0],
  [-45.3852,167.6192,"Luxmore Hut",4],


The last number corresponds to the hut categories:

0. Basic Hut/Bivvy
1. Standard Hut
2. Serviced Hut
3. Serviced-Alpine Hut
4. Great Walk Hut

This is the code you need to create clustered huts with custom markers:

The JavaScript map function, which converts one array into another, is not supported in Internet Explorer 8 and lower. If you need to support prehistoric browsers, use a for-loop instead. The icons I’ve used (which could have been more descriptive) are from Map Icons Collection.

The interactive map looks like this:

Fullscreen map

I especially like the animated feature of this clustering plugin (try zooming in and out), as it makes it more obvious for the map user what a cluster really is.

Whariwharangi Hut, built as a farmhouse in about 1896.


Connie said...

Hey.. I was wondering, you use the same variable name for the data if the huts (var hut) and for the marker cluster group, is that an error or is it okay?

Bjørn Sandvik said...

Hi Connie,

It was not intentional. I've renamed the first variable to "data".

kyle said...

hi, this is a really useful tutorial, thank you for posting it. I've been struggling with a way to cluster or spiderfy the markers on a map I made in which every marker has a unique icon and hover-over display text, and this is the closest I've found to some help.