Loading...

Follow GIS for Thought | GIS, Mapping, and Remote Sensing on Feedspot

Continue with Google
Continue with Facebook
or

Valid

I was once at an OpenStreetMap conference where 6 out of the 8 talks in one day had an image of the John Snow Cholera Map. And no surprise, it is an excellent, relatable, and interesting early example of GIS. The spatial relationship is unmistakable.

Original map overlaid on modern day London:

The site of the Broad Pump is now the location of a pub called the “John Snow”, which is well worth a visit if you are in London.

John Snow location:

John Snow Pub Sign with blue plaque Blue plaque Pump without handle memorial
  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

A follow up to my previous post: Every Person in Scotland on the Map. Winner of the 2016 OS OpenData Award for Excellence in the use of OpenData from the British Cartographic Society.

Full size interactive map.

The mapping process is pretty straightforward, and not accurate. I don’t know where you live. But I can make an educated guess.

I simply amalgamate the two sets of census data from the NRS (National Records of Scotland) for Scotland (2011 census) and the ONS (Office of National Statistics) for England and Wales (2010 census).

Postcodes were then created based on the ONS Postcode Directory, filtering for postcodes that were live in 2011 (which is the latest census data). The postcode centroids were turned into polygons using voronoi polygons.

Then we simply select all of the buildings in a postcode from Ordnance SurveyOpen Map product, filtering out most schools and hospitals. Then we put a random point in a random building for each person in that postcode.

I would have loved to include Northern Ireland, but the Ordnance Survey of Northern Ireland do not have an equivalent open building outline dataset, like Open Map from the Ordnance Survey.

Rendered with: QGIS tile writer python script. Processing done 100% in PostGIS.

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

The Struve Geodetic Arc is a chain of triangulation stretching more or less down the 26° E line of longitude from near Hammerfest on the Arctic Ocean over 2,820 km south to Izmail on the Black Sea. The survey was carried out between 1816 and 1855 under the guidance of F.G.W. Struve.

Theoretically, a degree of latitude is a constant and would have the same value at the equator as at the pole. But already Isaac Newton believed that the Earth was slightly flattened at the poles. This question of the shape and size of the Earth inspired the astronomer Friedrich George Wilhern Struve to come up with his famous Meridian Arc measurement.

The scheme included 258 main triangles with 265 not and over 60 subsidiary station points.The selection of points involves a total of 34 sites on the Struve Geodetic Arc. In today’s geography. the Arc passes through ten countries, viz. Norway (4 station points), Sweden (4), Finland (6), the Russian Federation (2), Estonia (3). Latvia (2). Lithuania (3). Belarus (5), the Republic of Moldova (1), and Ukraine (4).

All of the points in the Arc were designated as UNESCO World Heritage sites in 2005.

The site at Puolakka is easily accessible from central Finland, for example from Tampere, or especially Jyväskylä.

There is parking at the start of the walk, which is not maintained during the winter. But there is ample space on the roadside for parking. The path itself was in good condition but the road to the start could be difficult after a heavy snowfall.

The walk itself is 1km, all uphill. The path is very well maintained with stairs for the steeper sections. The view is definitely worth the time to visit.

Beginning of the walk. 740 meters to the start and 260 to the lookout tower Stairs on the path Lookout tower Triangulation pillar at the top View from the tower View from the tower Info board at the start of the walk Path map

Walk path:

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

In 2018 we started a running club at work.

I created a quick script to parse the data on Strava to a ShapeFile, which can be easily animated with QGIS.

The script only works with Garmin files, GPX, TCX, and FIT.

Source: https://github.com/HeikkiVesanto/Strava-Garmin-Parser

Example:

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

2018 was a very productive year for OpenStreetMap in Ireland.

Around 70k nodes added, 60k ways added, and 160k polygons added.

Finally a company was formed to facilitate becoming a fully fledged local chapter.

What does that look like day to day:

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

The Boundless PostGIS workshop is an excellent introduction to PostGIS. It can be argued that it is dated, but I think the fundamentals are still very valid. However maintaining a free course is quite an overhead for any company. So I don’t blame them from taking it down, and no longer hosted it on the Boundless website.

However it was released under a creative commons license and the source is easily available on GitHub, and can be easily built.

You can find a hosted version on: GISforThought.com/projects/postgis_tutorial/

The data can be found in my previous post: GISforThought.com/postgis-tutorial-data/

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

The OpenGeo (now called Boundless) PostGIS tutorial has long been my recommendation for people just getting started with PostGIS. It provides a broad intro to PostGIS, great for users new to SQL.

Unfortunately they recently removed it from their website. The guide was a fairly old now, so I don’t blame them. But it was a great free resource.

Luckily Archive.org has saved a copy of it. The course was based on open data, so compiling a similar dataset to complete the course was not difficult.

The course can be accessed at:

https://web.archive.org/web/20170913113658/http://workshops.boundlessgeo.com/postgis-intro/welcome.html

And the data can be accesses at (choose the green Clone or download button and Download ZIP):

https://github.com/HeikkiVesanto/postgis_course_data

I would skip the Loading spatial data chapter (very dated at this stage), and just use the ogr2ogr commands in the GitHub readme. Great chance to get started with ogr2ogr as well.

The data is also not 100% the same as the original. So some of the queries will have to be modified. Particularly the neighborhoods are different. So they may have slightly different names/boundaries/capitalization. So keep that in mind when creating your queries, and interpreting the results. But overall the data is pretty similar.

Also, if/when the Archive.org is gone that will likely be the end of the tutorial. So I would not waste any time completing the it.

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

I ran into a process where I wanted to create copies of rasters in PostgreSQL. While seemingly a simple process this took me a bit of work to figure out.

For my workflow I had three rasters, which all have the same size, and I want to load them into the same PostGIS table with three raster geometry columns. I don’t think this will work for different sized rasters since the rid’s will not match.

Three rasters:
raster1
raster2
raster3

Which I want to copy into:
merged_raster

First to create the merged raster table:

CREATE TABLE merged_raster
(
  rid serial NOT NULL,
  raster1 raster,
  raster2 raster,
  raster3 raster
);

Then to add the rid’s. These are the id’s of the tiles that the raster was split into when loading. If your tile size is large enough then you may only have one.

INSERT INTO merged_raster(rid)
(SELECT rid FROM raster1);

Then copying the actual data is straighforward (this assumes the raster column in the raster1 datasets is called rast):

UPDATE merged_raster m
SET raster1 = r.rast
FROM raster1 r
WHERE r.rid = m.rid;

UPDATE merged_raster m
SET raster2 = r.rast
FROM raster2 r
WHERE r.rid = m.rid;

UPDATE merged_raster m
SET raster3 = r.rast
FROM raster3 r
WHERE r.rid = m.rid;

Now I still have an issue that QGIS will not load these layers. It will always load the initial raster column no matter what is chosen.

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

Dublin has an official Monopoly board in time for Christmas.

Not to be confused with the Irish Edition of Monopoly. Which consisted of locations in Dublin with the addition of Shannon Airport.

Buy at:

Irish Edition

Dublin version

Full screen map.

Check out: MappingDublin.com

  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

Based on the work by:

Geoff Boeing: Comparing City Street Orientations

Rixx: Street Orientations

The graphs show the percentage of streets that run in a certain orientation. So for a grid based city like Chicago, there will be a heavy bias in north/south and east/west streets. Bearing in mind north and south will be the same (unless there are one-way streets, which only count in the direction they run in).

But for older cities that formed naturally, without modern city planning, the streets should be more varied.

Ireland:

Largest populated places by population. Based on the Ordnance Survey Ireland urban areas. As it is OSI data, Northern Ireland is not included.

Dublin Postcodes:

Some areas are clearly impacted by large motorways running through them.

And for non-Dubliners, a map of the postal district boundaries:

I updated the script by Rixx, so that it would take a ShapeFile as an input with a few caveats (it must be WGS84, it must have an attribute that has the are name and it must be called settl_name).

Check out the script at: GitHub

Read for later

Articles marked as Favorite are saved for later viewing.
close
  • Show original
  • .
  • Share
  • .
  • Favorite
  • .
  • Email
  • .
  • Add Tags 

Separate tags by commas
To access this feature, please upgrade your account.
Start your free month
Free Preview