More QGIS – Hurricane maps (lines to points and vector overlaps)

I posted a couple days ago about how I used QGIS to generate heatmaps of tornado activity based on raw point data.  Since I had invested time (kind of) learning the tool, I figured I should put together a few similar layers.

The most obvious choice was hurricane risk.  I ended up using a pretty similar procedure to when I generated the tornado heatmap, but massaging the data took a few extra steps:

  • The input data came as vectors instead of points
  • My data covered the whole globe, but I wanted the final vectors to only cover land areas

Again, I was happy with the result, so I figured I’d write it up.  

Similar to what I ran into with the tornado risk data, I couldn’t find any hurricane hazard GIS shapefiles.  I did again find a raw dataset of all hurricanes the NOAA has records on, which was enough to get started.

Importing all the vectors (I think there were about 700,000) from this MapServer took a while, and the result was, as expected, a bit cluttered:

There’s probably a better way to filter the data down, but I ended up exporting the records to shapefiles so I could filter on attributes.  The dataset had a lot of tropical storm data, and I filtered out everything except proper hurricanes (H1-H5).

Here things got a bit different.  The heatmap function I used for tornadoes only works on points, and these vectors were all lines.  Luckily, there was a brute force but straightforward solution: turn the line into a bunch of points.  QChainage is a simple plugin that does exactly that.  Once it’s installed, it’s available from the Vector  →  QChainage menu.

The above screenshot is a bit deceptive — I ended up using a point spacing of 20km in the final version.  The only main downside of a higher frequency is longer processing time when generating the heatmap. The result kind of looks a mess from above:

But looks a lot better once I zoom in:

From here, I’ll fast forward through the same stuff I did last time; I used the points to generate a heatmap, this time using 250km point radii, and pulled a vector out of it.  I iterated on thresholds until the most expansive layer more-or-less lined up with other reputable sources. My layer:

Compared to what I found online (source): 

Except for a few lumps in Virginia and Maine, it looks pretty comparable. 

Jumping forward a bit more, I again went with four gradients to get a map that looked like this:

I was a bit torn.  While this looks cool, the highlights on the ocean are distracting when the goal is to highlight risk areas on land; I needed to filter the shapes down to only land areas.

It turns out, intersecting vectors in QGIS is pretty easy.  I found a simple shapefile of all land areas on earth here (it wasn’t even a big download — less than 10MB).  Once this data was imported, I could use the Vector → Geoprocessing tools → Intersect tool to generate an intersection layer:

This did exactly what I wanted.  I repeated this for all four layers and ended up with a gradient only over land areas, exactly what I wanted.  I didn’t bother styling the layers, since I’ll just handle that in Mapbox later.

Just as a sanity check, I swapped back in the openmaptiles background to make sure the coastlines lined up correctly (they did, except a few hundred meters here and there on the coastline).

A nice bonus from this NOAA data: this time the data covered the whole globe.  All the other datasets I’ve found for other natural disaster risks are US-specific (and usually only the continental US):

I won’t go through the details on loading this into Mapbox; everything from here mirrored what I did last time.  You can see the result as a layer on bunker.land:

Once again I was pleasantly surprised at how easy it was to get (relatively) nice looking graphics from QGIS with minimal experience.  

At this point I’ve added data for most the layers I was interested in displaying (although I’m open to suggestions).  I’ll likely get back to the actual web-dev side of this project and clean up a few loose ends over the next couple weekends.

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