Back in 1962, archaeologists in the Czech Republic discovered a mammoth’s tusk that has been engraved with a geometrical design. The pattern was subsequently identified as representing the hills, rivers, valleys and routes of the surrounding area. It was dated around 250,000 BC, making it probably the earliest map ever discovered.
In the library of Hereford Cathedral is the Mappa Mundi. Created around 1300, it’s the largest surviving medieval map of the world. The UK’s Ordnance Survey was set up in 1791 to help address the perceived risk arising from the Jacobite rising, and of invasion by France, and it went on to become one of the world’s foremost national mapping agencies. And 1999 saw California-based ESRI release its ArcGIS graphical information system, which would become the world’s most used GIS (geographic information system).
These few notable dates in the history of cartography illustrate 27,000 years of change and it’s clear that the rate of change has accelerated significantly in recent years. This isn’t surprising since digital technology has had the same effect on so many other areas, but it’s been suggested that a GIS is so different to its predecessors that it’s a totally new entity. Professionals point to support of multiple layers and an ability to carry out analyses of geographically based data as just some of the things you can do with a GIS but not with an ordinary map. And if you’re wondering where Google Maps fits in, while we’re not going to get embroiled in the debate over whether or not it’s a GIS, we would agree with the sentiment that a fully blown GIS is like Google Maps on steroids.
ESRI’s well-respected ArcGIS isn’t cheap at £1,192 per year, including VAT, for professional use. This reduces to £139 for non-commercial use, but that’s still a lot unless you have a fairly serious application. Our subject here, therefore, is the free open source QGIS which is widely used professionally and is considered to be on par with many professional GIS offerings.
We’re going to provide a hands-on introduction to using QGIS but we’re certainly not going to be looking at all its features, in fact we won’t come close. After all, if you can think of something you believe you ought to be able to do with mapping data, it’s a fair bet that QGIS can do it, either natively or via one of its many plug-ins. However, we trust that our tentative first steps will be enough to excite you about the possibilities of QGIS and start you off on your own voyage of discovery.
If your main experience with digital mapping has involved Google Maps, the first thing you’ll notice when you start up QGIS for the first time is that you don’t see a map at all. Instead, unless you open a project that someone else has produced, you’ll need to create a new project but, even having done that, you’ll be faced with a blank canvas to which you’ll need to add data as layers.
Usually you’ll want to start a project by adding a base map so, let’s see how to do that, but first create a new project at Project>New. Now, in the Browser panel at the top-left, find and expand the XYZ Tiles entry and double-click OpenStreetMap. This will add the open source OpenStreetMap as a new layer. The map will appear in the main window and you’ll also be able to see it listed in the Layers panel at the bottom-left.
Although OpenStreetMap is the only base map shown by default, there are lots of others you can use, and you might like to familiarise yourself with what’s on offer. You’ll have to search out the URLs yourself, but as an example, right-click XYZ Tiles in the Browser panel and select New connection… In the Connection Details dialog, enter https://tile.opentopomap. org/%7Bz%7D/%7Bx%7D/%7By%7D.png as the URL, give it a name such as OpenTopoMap and click OK.
OpenTopoMap will appear below OpenStreetMap under XYZ Tiles and, if you double-click it, OpenTopoMap will appear as a second layer. In fact, it’ll appear to have replaced OpenStreetMap in the main window, but that’s only because it’s the top-most layer: it appears above OpenStreetMap in the list, and it’s fully opaque. We’ll look at opacity later but, for now, note that you can swap to seeing the OpenStreetMap again by clicking the tick box next to OpenTopoMap so it’s not displayed, or by dragging OpenStreetMap to the top of the list.
This method of adding base maps isn’t limited to maps in the normal sense of the word. You can also add satellite or aerial imagery using the same method. To add Google imagery, for example, use https://mt1. google.com/vt/lyrs=s&x=%7Bx%7D&y=%7By%7D&z=%7Bz %7D as the URL.
So far, we’ve seen how to add various layers to a QGIS project, although all of those layers were essentially images of one type or another. But since a GIS is concerned with far more than just images, or maps if you prefer, let’s take a look at how other types of data can be added.
To start we’re going to add some elevation data, but first a few words on types and sources. The types you’ll mostly find are DSMs (digital surface models) and DTMs (digital terrain models). DSMs include objects such as trees, buildings and cars, as well as the actual ground, while in a DTM the former types of object are filtered out so it represents only the topography. In the UK, elevation data has been produced by the Environment Agency at a resolution of 1m or 2m, and is distributed freely online by DEFRA. Over the Pond, the USGS makes elevation data available for the US at resolutions ranging from 10m to 30m, but with the aim of migrating to 1m. They also provide Space Shuttlederived data for most of the world at 30m resolution. Commonly elevation data is provided as a GeoTIFF file, which is a geo-referenced variant of the familiar TIFF image format, although there are other formats, and QGIS supports most of them.
Once you’ve downloaded the elevation data it’s time to import it into a QGIS project, ideally one into which you’ve already added a base map. Select Add Layer from the Layers menu and then choose Add Raster Layer… In the dialog, select the elevation data file by clicking the three dots against Raster Dataset(s) and clicking Add.
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