Shallow Thoughts : : Nov

A Smaller, Lighter Dataset: Clip Layers in QGIS

The dataset I used for mapping fire perimeters is huge: not surprising if it's all historic fires for the US. Classifying it in QGIS gave a warning, and operations were very slow. Here's how to clip a big dataset in QGIS to restrict it to a smaller geographic area.

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Tags: mapping, GIS, qgis, data
[ 11:43 Nov 27, 2023    More mapping | permalink to this entry | ]

How to Use QGIS to Identify Fire Areas

(A QGIS beginner's tutorial.)

For quite a while I've been wanting a map showing the perimeters of the big local fires. When walking through a burned area, I wonder, was this one from the Cerro Grande fire? Or Las Conchas? Or another fire?

Yesterday, inspired by Ryan Peek's #30DayMapChallenge toot on California Fire Perimeters, I decided to look for the data and load it in QGIS.

Also, I never did an entry for Day 3 of the #30DayMapChallenge, "Polygons", so this is it, not quite three weeks late.

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Tags: mapping, GIS, fire, Los Alamos, 30DayMapChallenge, openstreetmap
[ 12:34 Nov 23, 2023    More mapping | permalink to this entry | ]

Pixel 6a Stores the Wrong GPS in Images: an Analysis

I've been relying more on my phone for photos I take while hiking, rather than carry a separate camera. The Pixel 6a takes reasonably good photos, if you can put up with the wildly excessive processing Google's camera app does whether you want it or not.

That opens the possibility of GPS tagging photos, so I'd have a good record of where on the trail each photo was taken.

But as it turns out: no. It seems the GPS coordinates the Pixel's camera app records in photos is always wrong, by a significant amount. And, weirdly, this doesn't seem to be something anyone's talking about on the web ... or am I just using the wrong search terms?

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Tags: mapping, GIS, cellphone, google, programming, python, photography, 30DayMapChallenge
[ 19:09 Nov 20, 2023    More mapping | permalink to this entry | ]

Lost and Found: Missed the Mitchell but Found Something Unexpected (also, 30-day Map Challenge #15)

Yesterday's 30-Day Map Challenge theme was OpenStreetMap.

I use (and contribute to) OpenStreetMap quite a bit, and I use OSM basemaps in pretty much all my mapping. (I have used Google in the past, but between their changing or withdrawing APIs every few years, and suddenly deciding to charge for previously free APIs, I switched to using only open source maps.)

But that was yesterday, which was group hiking day, so I was out tramping over mountains instead of sitting at the computer making maps. But a wrong turn on the hike led to a serendipitous discovery that wouldn't have happened without OpenStreetMap.

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Tags: hiking, mapping, pytopo, serendipit, 30DayMapChallenge, openstreetmap
[ 11:08 Nov 16, 2023    More mapping | permalink to this entry | ]

Clayton Lake Dinosaur Tracks, Raton and the K-T Boundary

We've been taking some little 2- and 3-day trips to explore parts of New Mexico we haven't seen much. Last week, we visited Clayton and Raton, in the northeast corner of the state.

We'd been through Wagon Mound and Raton before but hadn't stopped. We'd never been to Clayton. Our goals were to see the dinosaur tracks at Clayton Lake, to try to find the Folsom site or the museum in Folsom, and to see what else the area had to offer. You don't know 'til you go.

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Tags: travel, geology, dinosaur
[ 18:30 Nov 13, 2023    More travel | permalink to this entry | ]

30-Day Map Challenge #5: An Old Paper Mountain Biking Map

Day 5 of the 30-Day Map Challenge is an analog map.

That got me searching back through old scans, and I found a couple good ones. In particular, some of my old El Corte de Madera maps.

El Corte de Madera Open Space Preserve is one of the open space parks in the Bay Area, above Woodside, CA. It's beautiful, dense redwood forest on a steep hillside. When I lived (and biked) there in the 1990s, ECdM (as it was abbreviated) was particularly popular with mountain bikers for its highly technical trails.

Unfortunately, not everybody agreed about those trails. The Mid-Peninsula Open Space District (MROSD), which administers them, had a policy that there should never be more than one trail going to any particular place, and it also had guidelines for trails that would have eliminated most of the technical ones. The official maps mostly showed the fire roads, which were especially steep, not at all technical, and generally not very interesting for biking.

But there were a lot of good trails at ECdM that weren't on the official MROSD maps. The property had once been used for logging, then for a while it was owned by a motorcycle (dirt bike) club, so there are all sorts of unofficial trails.

Mountain bikers passed around many-times-photocopied unofficial maps, some dating back to the motorcycle club days. One of my treasures in those days was a much-annotated map, marked up with ink of many colors, carried so much in my bike bag that it was coming apart at the folds. Of course, the hand-drawn trails are all approximate: none of us carried any sort of GPS then, and the GPS of the day probably wouldn't have gotten a signal in the deep redwood forests anyway.

In 2013 as we were preparing to move to New Mexico, I tried to find and scan old documents that were prone to getting lost during a move. I found a couple of old ECdM maps, though I'm not sure I found my main one; I remember it being more colorful than this one. Still, this one has a lot of my annotations, so I scanned it in case I lost the paper copy. Looking at it now brings back a rush memories of mountain biking adventures. And the map seems perfect for the 30-Day Map Challenge Day 5: Analog Maps.

Day 4: A Bad Map

By the way, although I didn't do any new work for challenge Day 4: A Bad Map, I wrote an article this past September wherein I go through several quite bad iterations of a choropleth map (regions shaded according to a particular variable — in this case a red-blue voting map) before figuring out how to get the colors right: Los Alamos Voting Data on a Folium Choropleth Map.

Tags: mapping, 30DayMapChallenge, MTB, bike
[ 15:23 Nov 05, 2023    More mapping | permalink to this entry | ]

Pytopo: Colorizing Lines According to Speed or Elevation (30 Day Map Challenge #2)

I've been wistfully watching the hashtag #30DayMapChallenge on Mastodon. For several years in a row, I've told myself I'm going to try the 30 Day Map Challenge ... and each time, I get busy with other stuff. And this year is no different.

So instead of trying to do all thirty exercises, I'll just do a few of the challenges when I have time and motivation. Better than nothing, right?

And as it happened, yesterday I got the urge to do a map-related project. Except it lined up with Day 2, whereas I didn't get it working til this morning.

So, two days late, here is my:

30 Day Map Challenge Day 2: Lines

During a bike ride along the fast section of one of our fantastic White Rock trails, I found myself wishing I could view my track logs colorized according to how fast I was going. And I realized that I could pretty easily add that to PyTopo's track log displaying code. And as long as I was doing that, why not also add the ability to colorize by elevation as well?

Most GPX track logs already include elevation (though the ones I get from OsmAnd aren't super accurate: they're GPS elevation rather than using the barometric sensor that some phones have). Track logs from OsmAnd sometimes include speed, via the nonstandard construct

        <extensions>
          <osmand:speed>0.3</osmand:speed>
        </extensions>

which PyTopo already knows how to parse; and of course, for track logs that don't include speed, it can be calculated according to the distance and time difference from the previous track point.

Indeed, it was pretty easy to add. I put it on the context menu as a new submenu, Colorize Tracks.

I probably should play with the colormaps and use something smarter than a simple blue-to-red gradient, but even as it is, it's fun to look at a hike to Nambe Lake colorized by altitude (first image) or a mountain bike ride along Potrillo Mesa and the Boundary Trail colorized by speed (second image).

The code is on GitHub, in this commit.

Again, that's for the challenge two days ago. Today's Map Challenge is "A Bad Map". No promises that I'll have time for another mapping project today ... but I'm looking forward to seeing what other people come up with.

Tags: mapping, GIS, 30DayMapChallenge, pytopo
[ 12:28 Nov 04, 2023    More mapping | permalink to this entry | ]