Jim Clifford, Josh MacFadyen, and Daniel Macfarlane

In this lesson you will learn how to create vector layers based on scanned historical maps.

edited by

  • Adam Crymble

reviewed by

  • Finn Arne Jørgensen
  • Peter Webster
  • Abby Schreiber

published

2013-12-13

modified

2013-12-13

difficulty

Medium
This lesson is part of a series. You might want to check out the previous lesson.

Contents

Lesson Goals

In this lesson you will learn how to create vector layers based on scanned historical maps. In Intro to Google Maps and Google Earth you used vector layers and created attributes in Google Earth. We will be doing the same thing in this lesson, albeit at a more advanced level, using QGIS software.

Vector layers are, along with raster layers, one of the two basic types of data structures that store data. Vector layers use the three basic GIS features – lines, points, and polygons – to represent real-world features in digital format. Points can be used to represent specific locations, such as towns, buildings, events, etc. (the scale of your map will determine what you represent as a point – in a map of a province, a town would be a point, whereas in a map of a town, a building might be a point). Lines can effectively represent features such as roads, canals, railways, and so on. Polygons (effectively enclosed shapes with more than a few sides) are used to represent more complex objects such as the boundaries of a lake, country, or electoral riding (again, scale will affect your choice – large buildings in a close-up map of a city might be better represented as polygons than as points).

In this lesson you will be creating shapefiles (which are a type of vector data) to represent the historical development of communities and roads in Prince Edward Island. Each shapefile can be created as one of the three types of features: line, point, polygon (though these features can’t be mixed within a shapefile) . Each feature you create in a shapefile has a corresponding set of attributes, which are stored in an attribute table. You will create features and learn how to modify them, which involves not only the visual creation of the three types of features, but also the modification of their attributes. To do so, we will use the files from Installing QGIS 2.0 and Adding Layers concerning Prince Edward Island.

Getting Started

Start by downloading the PEI_Holland map to the project folder:

Open the file you saved at the end of Installing QGIS 2.0 and Adding Layers. You should have the following layers in your Layers window:

Uncheck all of these layer except for PEI_placenames, coastline_polygon and PEI_CumminsMap1927

Figure 1: Click to see full size image.

Figure 1: Click to see full size image.

We are now going to add a second historical map as a raster layer.

Figure 2

Figure 2

Figure 3

Figure 3

In previous steps you have selected and unselected layers in the Layers window by checking and unchecking the boxes next to them. These layers are organized in descending order of visibility – i.e. the layer at the top is the top layer in your viewer window (provided it is selected). You can drag the layers up and down in the Layer window to change the order in which they will be visible on your viewing window. The coastline_polygon raster layer is currently not visible because it is below the PEI_HollandMap1798 and PEI_Cummins1927 layers. In general it is best to keep vector layers above the raster layers.

Uncheck PEI_Cummins1927 so that the only layer you have remaining is PEI_HollandMap1798. Note that the map appears crooked on the screen; this is because it has already been georeferenced by the lesson writers to match the GIS vector layers. Learn more about georeferencing in Georeferencing in QGIS 2.0.

Figure 4

Figure 4

We will now create a point shapefile, which is a vector layer. Click Layer -> New -> New Shapefile Layer

Figure 5

Figure 5

After selecting New Shapefile Layer, a window titled New Vector Layer appears

Figure 6: Click to see full size image.

Figure 6: Click to see full size image.

Returning to the New Vector Layer window, we are going to make some attributes. To create the first attribute:

Now we are going to create a second attribute:

For the third attribute:

Figure 7

Figure 7

Note that a layer called ‘settlements’ now appears in your Layers window. Relocate it above the raster layers.

Figure 8

Figure 8

Uncheck all layers except settlements. You will notice that your viewing window is now blank as we have not created any data. We will now create new data from both the PEI_HollandMap 1798 and the PEI_CumminsMap1927 to show the increase in settlement between the late 18th and early 20th centuries.

Figure 9

Figure 9

Figure 10

Figure 10

We will now repeat the steps we took with Charlottetown for Montague, Summerside, and Cavendish (again, you can find these locations by adding the PEI_placenames layers). Find Montague on the map, select the 3 dot feature button and click on Montague on the map. When the Attributes window appears, input Montague and 1732 in the appropriate fields. Repeat for Summerside (1876) and Cavendish (1790).

Figure 11

Figure 11

In the Layers window, unselect the PEI_CumminsMap1927 and select PEI_HollandMap1798. We are now going to identify two settlements (Princetown & Havre-St-Pierre) that no longer exist.

Figure 12

Figure 12

On the northern coast of Lot 39 between Britain’s Pond and St. Peters Bay, we will now put a dot for the location of a long lost village called Havre-St-Pierre.

Figure 13

Figure 13

We will now now create another vector layer – this layer will be a line vector. Click Layer -> New -> New Shapefile Layer. The New Vector Layer window will appear (in the Type category at the top, select Line)

Create a second attribute

We are now going to trace the roads from the 1798 map so that we can compare them to the modern roads. Make that you have the PEI_Holland1798 and settlements layers checked in the Layers window. Select road layer in the layers window, select Toggle Editing on the top toolbar, and then select Add Feature

Figure 14

Figure 14

Figure 15

Figure 15

Deselect the PEI_HollandMap1798 in the Layers window and select the PEI_highway map. Compare the roads represented in the PEI_highway map (the red dotted lines) to the roads you have just traced.

Figure 16

Figure 16

Now create a third type of vector layer: a polygon vector. Click Layer -> New -> New Shapefile Layer. The New Vector Layer window will appear – in the Type category at the top, select Polygon

Create a second attribute

Figure 17

Figure 17

Start by creating a polygon for lot 66, which is the only rectangular lot on the island

Figure 18

Figure 18

We are now going to trace lot 38, which is just west of Havre-St-Pierre. Make sure that there is a check mark in the box beside PEI_HollandMap1798 layer in the Layers window

Click on Toggle Editing on top tool bar, and then click on Add Feature

Trace the outline of Lot 38, which is more difficult because of the coastline, as accurately as possible. In order to show you the Snap feature, we want you to trace along the modern coastline (snapping is an automatic editing operation that adjusts the feature you have drawn to coincide or lineup exactly with the coordinates and shape of another nearby feature)

Figure 19

Figure 19

Figure 20

Figure 20

Make sure that the lots layer is selected in Layers window, and select Add Feature from the tool bar

Figure 21

Figure 21

When you finish tracing and creating the polygon, select and deselect the various layers you have created, comparing and seeing what relationships you can deduce.

In Google Earth there were limitations on the types of features, attributes, and data provided by Google, and Google Earth did much of the work for you. That is fine when you are learning or want to quickly create maps. The advantage of using QGIS software to create new vector layers is that you have a great deal of freedom and control over the types of data you can use and the features and attributes that you can create. This in turn means that you can create custom maps far beyond what can be achieved in Google Earth or Google Maps Engine Lite. You have seen this firsthand with the points, lines, and polygons vector layers you learned how to create in this lesson. If you found data on, for example, public health records in the 18th century, you could create a new layer to work with what you already created showing the distribution of typhoid outbreaks and see if there are correlations with major roads and settlements. Moreover, GIS software allows you to not only spatially represent and present data in much more sophisticated ways, but to analyze and create new data in ways that aren’t possible otherwise.

You have learned how to create vector layers. Make sure you save your work!

This lesson is part of the Geospatial Historian.

Great! Now you're ready to move on to the next lesson .
About the authors

Jim Clifford is an assistant professor in the Department of History at the University of Saskatchewan.   Josh MacFadyen is a Project Coordinator at the Network in Canadian History & Environment.   Daniel Macfarlane is a Visiting Scholar in the School of Canadian Studies at Carleton University.