GIS for Cave Surveyors Part 2

This second article will cover the steps I used in a recent project to produce a GIS map of the caves of the Peak District, from collecting and modifying  the location data for the caves to creating contours for the area covered. It is not intended as a tutorial for QGIS although it may be used as such. Better tutorials are available on the internet.

The initial date were derived from a GPS set on the Peak District Caving website. The data files can be downloaded as Google Earth, Garmin GPS, Memory Map or a GPX file. In this example I will use the Google Eath kmz file.

Quantum GIS can import the following vector files

You will notice that kmz files are not included in this list. That's not a problem we can use Google Earth to convert it. Double click on the file and it should open in Google Earth.

 

Right click on the layer and choose Save Place As then select file type kml. Save the file somewhere on your hard disc.

Now, back in QGIS select Layer from the main menu and, from the drop down click on Add Vector Layer

In the source type drop down select the File radio button and then click on the Browse button

Browse to the kml file you saved from Google Earth. Don't forget to change the file type in the drop down at the bottom to KMLClick on Open.

Now Open in the File Type window. A new layer will be created in QGIS with all the caves shown as  coloured dots.

 


To add labels to your map double click on the layer PeakCaves (or whatever you named it). This will open the Properties window for that layer.

Click on Labels in the left hand menu list. Tick the Label this layer box and select name from the list of fields. Click on OK and all your caves will have labels.


 

Attributes is another name for the contents of data fields. Right click on the layer name and select Open Attribute Table.

 

You will now see a table containing the names and descriptions of all the points in the layer. These values were assigned in the original kmz file.


So far we have produced a map showing the cave locations but this is useless unless we can relate it to the real world.

We can achieve this by adding a coordinate grid. We do this at the output stage which I'll get to later.

In the meantime we can add contours but first we need to get some terrain data. These data are DEM's or Digital Elevation Models which are available from various sources. I get mine here.

Download the area in which you are interested and import into QGIS from the Layer - Add Raster Layer menu selection. Point the file browser to the DEM you download, a filename something like this ASTGTM_N53W002_dem.tif.

You should now have something like this

 This layer consists of a tiff file with each pixel having an altitude attribute. We can extract these altitude data and create contours from them. Click on Raster - extraction - contour and a dialogue window will open

Enter an output filename , select a contour interval and click OK.

Turn off the DEM layer and you should now have something like this


 Now we can have a look at the output.

Click on Project -  New Print Composer

Enter a name for the Composer and the Composer Window will open

The first thing to do is add a map. Click on the Add New Map icon just over halfway along the toolbar and click and drag a rectangle on the composer canvas. A copy of the current map view will appear.. This can be modified in the properties window on the right but I'll leave you to learn this from a QGIS tutorial. For now I'll just show how to add a grid.

Click th Show grid button and enter suitable properties for the grid

Your map should now have a grid

Play with the grid properties until you're happy and then you can export your map by clicking on Composer - Export As...

 

Job done, but...

This has barely scratched the surface. GIS can do much more than produce a half decent map. There are loads of tutorials on the internet.