Making Grids for North Arrows and Scale Bars
No one gets tattoos of scale bars. They’re not nearly as pretty as a compass rose, you never see as much variation or style in them and I think the best that can be said for them is that you can tuck them out of the way and forget about them until the user makes a pinching gesture with their thumb and forefinger and awkwardly counts out a rough distance. Unless you’re making blueprints, scale bars are never going to be used precisely- they’re really just for orienting the audience and helping them eyeball the image but I started using grids for my dive series of maps on Opendivesites.org and I think I’m going to use them more in other maps too.
There’s nothing new about using grids. The cool kids are still making hex-bins to chunk and summarize complex data sets and quadrangles have been used for centuries to divide equal areas into manageable pieces or pages but I still don’t see many maps using grids for scale.
Since I’m printing my maps onto standard A1 letter pages, I wanted the edge of the paper to align to True North so that the image itself is oriented in a way that the audience is familiar seeing it, but I rotated the grid to align with magnetic north because my audience uses magnetic compasses and rarely correct for declination since headings are often communicated magnetic. A grid lets me replace a scale bar and north arrow at the same time
Zoomed in maps with small extents aren’t really affected by projection distortion so the square patterns are pleasingly geometric and the lines can be hidden and faded under other features across the whole canvas in a fairly unobtrusive way. You can follow the lines of the squares or you can follow the spaces and it’s very easy to gauge distances in two different axes at the same time without the needs for a ruler or a finger to trace the map distances. In applications like instruction where a teacher is pointing out features on a paper map held out for others to see, the students might be a few feet away but they can still count square and measure distances by eye without having to physically interact with the map- a thing that makes this approach more accessible in some circumstances. A person with limited dexterity might struggle to use a scale bar adequately.
There aren’t any standard north arrows or scale bars that utilize grids so I made my own in Inkscape where I was making the rest of my map. I’m not completely sold on it but the folks I’ve showed it to like it once I point it out. What it lacks in intuitiveness it seems to make back in utility. Let me know if you have a good solution to this!
There are two major ways to use these regular grids. You can use them to measure out spaces like on a chess board or on a D&D campaign map where you might trace out a distance by placing your finger or playing piece in a square and moving it to adjacent squares.
Or you can use the grid as a measuring stick more like a line of latitude or longitude. The actual shape of the grid spaces is unimportant because you can see on a globe that two dimensional geometry gets a bit warped on a sphere anyway. Squares become quadrangles whereas lines can still be straight or at least mark a constant bearing which is especially helpful for folks using compasses.
And we can create grids with different shapes too.
- Triangles create three axes if you follow along the uninterrupted straight lines but the spaces don’t suggest straight lines or constant distances and the angles don’t conform to the compass rose.
- Square grids create two axes which work well for North-South and East-West applications that follow compass orientations and whether you use the spaces or the lines to measure distances is irrelevant. It’s very easy to make and use for a variety of applications.
- Pentagons don’t tesselate evenly. You get these weird little parallelograms. I’m not sure what to do with these.
- Hexagons don’t create any unbroken axes so they’re not as good as scale lines but they’re good for counting regular shapes to measure distances in three axes. Hexagons are a perfect complement to triangles this way.
- Octagons don’t tesselate either- you end up with little squares in the corner and they only have two axes that aren’t interrupted by them. Also not very useful.
But any radially symmetrical pattern can be used to measure distances like trying to count how many sheets of wallpaper were used to cover your wall by counting the repetition of the pattern- it’s just that the more complicated the pattern, the harder it is use and the more the shapes clash against the actual content features of the map. For a map of a big open space where you simply want to demonstrate scale, why not use a crazy tessellation pattern to fill the negative space? You could even use an irregular pattern of bears like Annukka Makijarvi did in her map of Finland.
There should be more grids for cartographers.
And I think we should be looking more to the quilting and crafting communities for inspiration.
Anyway, here’s how to make a grid in QGIS:
- Create a grid with polygons using the Vector>Research Tools>Create Grid
- Look up the magnetic declination for your map extent. I like this website from Natural Resources Canada. Just type in your lat/long and get your declination.
- Select all of the squares in your new grid and edit the layer. Click somewhere in the middle of the grid and use the Rotate tool to adjust the grid by the appropriate declination
- Set the grid style to “no fill” and style the outline.
- I tried a few times to clip my grid to the shoreline so that only the water has a scale grid but I ended up creating a faded land mask in GIMP and using it as an overlay so that the grid seems to fade into the shoreline.
- Make a Key in your favorite vector tool. GIS software can’t help you now!