Recreating Topographic Maps in QGIS ¶

For a while now I have been trying to simulate the 1in50k topographic maps of South Africa. I started using QGIS since version 1.8 and I couldn’t replicate the cartography on the topographic maps but over time as QGIS has matured, I could replicate the NGI maps. NGI uses proprietary software and then Adobe to fine-tune some context on the maps. For this exercise I used QGIS 3.12.0

The goal of the exercise was to emulate the grid labels for the topographic maps as depicted below.

I navigated to the map composer and added my grid with the following properties.

Custom Grid Labels ¶

In labeling, I choose custom settings and then used the following formulae:

CASE
    WHEN  @grid_axis = 'x' THEN
        IF (  to_dm(  @grid_number , 'x', 0) != to_dm( x(transform( point_n( @map_extent , 1), 'EPSG:3857', 'EPSG:4326' )), 'x', 0),
            IF (  to_dm(  @grid_number , 'x', 0) != to_dm( x(transform( point_n( @map_extent , 2), 'EPSG:3857', 'EPSG:4326' )), 'x', 0),
                right(to_dm(  @grid_number , 'x', 0),3), to_dm(  @grid_number , 'x', 0)) , to_dm(  @grid_number , 'x', 0))
    WHEN @grid_axis = 'y' THEN
        IF (  to_dm(  @grid_number , 'y', 0) != to_dm( y(transform( point_n( @map_extent , -4), 'EPSG:3857', 'EPSG:4326' )), 'y', 0),
            right(to_dm(  @grid_number , 'y', 0),3), to_dm(  @grid_number , 'y', 0))
END

Breaking Down the Functions ¶

1. We get the grid axis we need to label using the expression @grid_axis = 'x'

2. We then get the grid number of the graticule and we compare it to the starting point of the geometry of the grid which we find using the expression point_n( @map_extent , 1)

3. If the values are equal we then label the grid using the decimal value for the grid. If not then we label using the minutes for the grid.

4. To get the second corner coordinate we use the expression point_n( @map_extent , 2) which gives us the geometry of the point at the second position of the polygon extent of the map.

5. We nest the if functions so that we can get the function listed above.

This approach demonstrates the powerful data-defined capabilities in QGIS 3.12 for creating professional cartographic outputs that match official topographic map standards.