Vectorizing Historic Maps in QGIS

This tutorial provides detailed, step-by-step instructions for digitizing features from raster (image) maps to create new vector data in QGIS. This process is essential for transforming historical maps or scanned images into analyzable geospatial datasets, enabling you to conduct spatial analyses like area calculations and attribute queries.

Set a Project Coordinate Reference System

1. Download QGIS.
2. Create a new QGIS project.
3. Add a basemap to the project by going to the Browser panel, expanding XYZ Tiles and double-clicking OpenStreetMap.

   If you do not see a browser panel, you can go to the program menu at the top of the screen and select View → Panels and turn on Browser.

4. The project coordinate reference system should now reflect that of the basemap we just added. In the bottom-right hand corner of the QGIS window, find the button that says EPSG: 3857. Click that button to open the Project Properties - CRS window.

You can search for coordinate reference systems by name, place, or EPSG code. You will want to choose a projection that is suited for the area you are creating data for, and is measured in units such as meters or feet, if you want to do area calculations. You can find this information in the properties of each coordinate reference system.

5. Zoom in to the area of interest using the Zoom buttons.

6. If the map disappears when you move it, or looks as though it is a strange shape, it could be due to the software attempting to reproject the basemap to the shape of a coordinate reference system built for the location you have chosen. Wait for the screen to re-load, or you can zoom to the extent of the basemap by right-clicking OpenStreetMap in the layer list, and choosing Zoom to Layer. Continue zooming until the area of interest is centered on the map. Any notifications about ballpark transformations you can click through or ignore.

Import Georeferenced Maps

• If you have a .geoTIFF, you should be able to drag the file directly into the QGIS document and have it show up in the correct place.
• If you do not yet have a georeferenced map you'd like to work with, please refer to other guides on this pre-requisite step. A useful place to start is our Georferencing in QGIS tutorial. You can also make an appointment at the Map Collection.

Create New Shapefile Layer

1. Click on Layer > Create Layer > New Shapefile Layer.
2. Select Polygon as the geometry type.
3. Important! From the coordinate reference system menu in this interface, ensure you are creating the new shapefile in the coordinate reference system you selected.

4. Add necessary fields for the attributes you want to record. These fields will become the column headers in the data table you will create. For every polygon you create, you will also fill out a value for each of these attributes.
5. Pay attention to field types. If you are recording categories or text data, make sure you select Text as the field's data type. If you are recording a number you'd like to be able to symbolize by density, make sure to select Number as the field type.

Draw Polygons on the Map

1. Start drawing polygons by clicking on the Toggle Editing button, which looks like a pencil.

2. Select the Create Polygon button.

3. Start drawing!

This takes a little bit of practice to get used to. To make it easier, use the snapping tool to make sure your lines and vertices match up, and don't leave any holes between your polygons.

4. In the main QGIS menu choose Project then Snapping Options. Toggle on the magnet icon on the far left of the wizard. Turn on Vertex and Segment. Turn on Topological Editing and Snapping on Intersection so that both buttons are engaged.
5. You can right-click your in-progress data layer in the Layer panel, and choose View Attribute Table. This will show you each polygon as a row in the table, and you can edit the values there.
6. Any changes you don't want to lose, make sure to Save by continuously clicking the Pencil or Toggle Editing icon.
7. To really learn the true ins and outs of everything you can do with the editing toolbar, including moving or deleting points, check out the QGIS Editing Documentation.