Cartography – not a big part of Geog 204
In this class, we have not paid much attention to cartography and many of the topics associated with it. For our projects we will have to make maps of course , but we are more concerned about analysis than map making. We played around with map composers in QGIS, but unless you took Geog 205, you will not be aware of cartographic conventions\practices.
It is important to be familiar with projections, as it is generally beneficial to have all your data in the same projection for overlay analysis. QGIS and ArcPro have made steps towards compensating for projection differences during analysis, but it is better to use the same projection for project data.
We will go over some of these principles in upcoming tutorials.
We have to know something about them (even if we make ugly maps)
Another cartographic principle that we have not discussed in this course is map projections. Map projections are a method by which map content can be transposed from the spherical world to flat two dimensional maps. There are many projection techniques that have been created and developing for hundreds of years.
You may be finding that with your project you are coming across data that does not have x and y positions in Latitude and Longitude, but other data layers do. In this tutorial we are not going to discuss the theory of projections too deeply (we are going to skip Geodes, Datums and Ellipsoid) , but we are going to get an idea as to how it works.
USGS Projection Poster
USGS will of course be dealing with different projections across the US. In Canada, we are in the same situation – lots of area to cover. With the large land mass of Canada, many different projections are used across the country. We will look at this poster in a bit of detail to get a handle on the projections we will see most common in this course.
Check out the USGS Poster
Using Projections in QGIS
Taking turns loading data into our projects
Open QGIS and load a web tile layer from the QuickMapServices Plugin. Zoom into Canada. What is the value in the bottom right of QGIS – EPSG Code (the European Petroleum Standards Group – now defunct – but the projection codes live on).
Check out the properties of this layer. What is the projection of this layers?
Load in the StatsCan provincial boundary shapefile in
What do you think of the size of Ellesmere Island and Greenland? Africa and Greenland look the same size (good old Mercator).
Data Quality check:
Zoom to the border between BC and Alberta. Set the StatsCan layer semi-transparent to compare the borders from the web tile and Stats Can.
How do they compare – in terms of accuracy and precision?
Start and new project
Start a fresh project and load the same Stats Can Layer into your canvas (don’t bother saving your other project). Load in the same web tile again.
How does Greenland look now?
If you zoom out – how does South America compare?
Start another project and load in the BC Boundary geopackage in:
Choose the singlepart layers from the layers in the GeoPackage
What projection is this layer and our canvas?
Load in the StatsCan Provincial boundary.
Do the layers line up?
If they do line up – what about accuracy and precision.?
This inability to project the data into the same geographic space would really screw up analysis (as they are not in the same place.
Projecting your data to ensure analysis works out
Let’s try our hand a re-projecting layers:
- Start a new project and load in the StatsCan province boundary layer.
- Select the features of BC and Alberta (both provinces)
- Save the selected features as any format you wish – BUT
- Select the output projection as 3005 (BC Albers projection)
Start another project once more. Load in the new BC Alberta layer and the BC Border geogpackage layer. How do they line up now?
Go to the Open Data Prince George page and download the Road centerlines as a shapefile. Unzip the download and open the .prj file in workpad or notepad.
What is the projection of this data?
How can you find out the EPSG code for the layer – load it into QGIS and check it there?
Save this road layer in the same projection as the BC Border GeoPackage
Downloading Provincial data and its Metadata
The BC Border layer we are using is at:
What metadata can we find in this page?
Custom downloads from BC
- Hit the Geographic Dataset button (Green button) on the top left of the page.
- Then select the “recreational sites and trails” dataset from the list (or search it out)
- The dataset can be found at:
- Choose the “BC Geographic Warehouse Custom Download” link
- Access/Download button
- Allow popups
You should get a popup with a form to fill in. Fill in the panel as below (with your email):
You will get two emails from Data BC; one letting you know your order has been submitted and one for downloading the data.
ESRI File Based GeoDatabase
Once you unzip the downloaded file, you will see metadata files (i.e. the html file) and a folder with a .gdb extension. The data is actually in the folder. If you navigate to the folder with QGIS browser of the catalogue in ArcPro, you can find the recreations area boundary layer to add to you project (the one starting with WHSE).
Go the the web page for projection information for WGS 84 at http://spatialreference.org/ref/epsg/4326/
Now look up the value 32610 in the search panel at spatialreference.org – does this make sense as a projection for where Prince George is? You notice there is a list of files used to describe this projection depending on software and standards. What file would be used with shape files that QGIS can use to determine its projection? Is there one for the roads layer? Does it match the one at spatialreference.org?
Try 32710 – what is that projection?
Try 900913 -what is it? Why was Google so instant that they have their own projection labeled by the EPSG as this number?
What does EPSG stand for? Check out EPSG