Exercise 2: Create a point index map from a spreadsheet containing coordinates

Many collections of historical aerial photos have not been fully georeferenced, but there may exist rough latitude/longitude coordinates for each photo. In this exercise, we’ll take a spreadsheet containing coordinates and turn it into a point-based index map.

1. Load the spreadsheet

Adding a CSV in this manner will treat all fields as text strings, which is okay, because we are going to use the Refactor Fields tool anyway, at which point we can specify the data types.

Spreadsheets in the form of .xlsx Excel files could also be used, in which case QGIS should automatically respect the cell types.

2. Turn the rows into points

In this example, the columns are WGS 84 longitude and latitude. If your data has x/y values in a different coordinate system, be sure to select the appropriate CRS.

3. Explore the data

Let’s explore the values of some of the columns by setting the point color from one of those columns.

Categorized by county

Try categorizing by year, and notice how photos from different years were used to fill in gaps. (This is why we aren’t planning to separate out different years into different files.)

4. Refactor fields

Use the “Refactor fields” tool to rename or delete several of the fields:

refactor fields dialog

5. Save as GeoJSON

Now we have all the points saved to a single GeoJSON file.

6. Save a GeoJSON for each county

What if we wanted to save each county separately, based on the “county” column?

Next: Exercise 3