Using QOSM to provide OpenStreetMap basemap in QGIS for my slopelines project

In previous posts I have described how I have used a segmented DEM with RSGISlib, a method originally developed as part of my MSc dissertation on Martian glaciers, for visualising slopes on Earth.

I have been looking at these again, and have produced a few maps with the QOSM plugin, which dynamically loads OpenStreetMap tiles into QGIS.

These maps below were produced with the Thunderforest Outdoors rendering. The slopelines are as previously, red for convex slopes, blue for concave, with thicker lines denoting steeper slopes.

Previous versions of this had used a version of OpenStreetMap that I was preparing myself from the source data within QGIS. Using the basemap tiles I can focus on adapting the visualisation of the slope lines themselves a bit more.

Bodmin Moor

Camborne and Redruth, including Carn Brea and Portreath

Penzance

Truro

A close up of Truro

For a while I thought the QGIS bug I found had recurred which meant that the arrows had disappeared. However it was something wrong in my data dependent styling, not sure how it happened. Once fixed, I show the slope direction with arrows, which is only possible up to about 1:10,000 otherwise the rendering struggles:

Indicating the downslope direction with arrows.

Delabole, showing the slate quarry.

St. Ives

Aberystwyth, Wales

Cadair Idris, Wales

A wider view of Cadair Idris, too small a scale to allow plotting the arrows.

Pen y Fan, Brecon Beacons, Wales

A bit more on geomorphons, varying the 'inner search radius'

I had originally posted maps of DEMs of Cornwall and the Aberystwyth area of mid-Wales processed using Tomasz Stepinski et al.'s geomorphon method as descibed in the papers of: Stepinski+Jasiewicz 2011, Jasiewicz + Stepinski 2013.

Since then I have become aware of the 1 arcsecond SRTM data being available, so I have recalculated the geomorphons and here show the map of the same area of mid-Wales that the landcover assignment from my MSc was concerned with.

Using the search distance L=1500m, as did T. Stepinski in his geomorphon map of Poland (user guide), I varied the 'inner search radius' which determines the minimum distance the software looks, using 0, 2 and 4 cells. 1 cell is ~ 24m in the SRTM 1 arcsec data after conversion to OS grid reference coordinates.

Inner search radius 0m

In some of the flatter areas results are difficult to interpret. full-resolution image.

Inner search radius 2 cells (~50m)

Looking in Borth Bog, more of the area is shown as 'Flat' full-resolution image.

Inner search radius 4 cells (~100m)

As the inner search radius is expanded to 4 cells, most of the possibly spurious peaks in the flat area of Borth Bog disappear. full-resolution image.

I expect it would be interesting to combine it with the segmentation and classification with RSGISlib and to examine correlations between the landscape position of a location, and the land-cover.

Revisiting geomorphons - with 1 arcsecond SRTM data

I had originally posted maps of DEMs of Cornwall and the Aberystwyth area of mid-Wales processed using Tomasz Stepinski et al.'s geomorphon method.

Since then I have become aware of the 1 arcsecond SRTM data being available, so I have recalculated the geomorphons and present some maps of Cornwall here.

I've also become more aware of the various layer blending methods in QGIS which has allowed me to blend it with a hill-shaded topography layer.

In these maps, the search distance L = 1500m, flatness threshold 1 degree.

West Cornwall. Full resolution image.

SE Cornwall, Tamar valley and Dartmoor. Full-resolution image.

North Cornwall. Full-resolution image.

Minimum search radius

It is possible to specify an 'inner search radius' that ensures a minimum search radius for the geomorphons. In the maps below, using a minimum search radius of 2 cells (about 50m for this data), this makes the map look a little less noisy:

West Cornwall. Full resolution image.

SE Cornwall, Tamar valley and Dartmoor. Full-resolution image.

North Cornwall. Full-resolution image.

Some more work in progress re: Cornish GIS maps

Here is a little more about my work in progress in generating maps of Cornwall in QGIS.

I have downloaded various Ordnance Survey VectorMap data, along with some layers which come from OpenStreetMap. The OS VectorMap has layers including woodland, tidal water, surface water polygons (e.g. lakes and reservoirs), foreshore and surface water lines (rivers etc.) and others.

These is more comprehensive than OpenStreetMap, however the OpenStreetMap vector layers come with names associated with them in the attribute table in some cases. Certain of the OS VectorMap layer objects will exist in the VectorMap 'Named Places' shapefile, but as points rather than as names in the attribute tables of the polygons themselves.

In the map below I have used the woodland polygons from the OS VectorMap and the ones from OpenStreetMap, but only the OpenStreetMap ones are labelled, since only they have names in the table.

I have also generated contours based on the Shuttle Radar Topography Mission, 1 arcsecond data, which is now freely available for most of the world. It is also possible to use OS Terrain50 contours, which generally appear smoother than these ones, however given these are released in individual squares, I found myself having so many vector layers in the rendering that QGIS crashed.

The Falmouth area, using contours from SRTM 1 arcsec

There is a fairly large amount of data entry to be done to put the names in Cornish, and beyond the list that has already been published by MAGA I would expect it to be slower work.

The OS VectorMap Named Places shapefile for the SW grid square has 2759 entries, of which 679 are various geographic features and the remainder are populated places.

The OpenStreetMap files have approximately 122 named woodlands in Cornwall (of 810 polygons, of over 9000 in the SW grid square alone for OS VectorMap), 56 named water polygons (of 327), 21 parks (of 45), 242 named waterways (of 2923) as lines (some duplicate names for different parts of a feature), and 1337 named places (of which I have already entered 421 in Cornish based on the MAGA Kernow list). There are 10342 named roads in Cornwall from the Open Street Map data.