Making Grids for North Arrows and Scale Bars

A 100 yard scale grid oriented to magnetic north
A typical dive compass is too chunky to place on a map and do sophisticated orienteering. As a result, headings are almost always communicated magnetic.
A revised grid scale/north arrow combo. People seem to find it a little confusing at first but reasonably effective.
Found here: https://media.wizards.com/legacy/dnd/images/dng_coastal-lair.jpg
  • 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.
Why not Escher? https://www.scientificamerican.com/article/when-scientific-american-made-m-c-escher-famous/
Not hexagons. Texagons. https://i.pinimg.com/originals/7f/ce/22/7fce2251e07253ed28520605326b35fc.jpg

Anyway, here’s how to make a grid in QGIS:

  1. Create a grid with polygons using the Vector>Research Tools>Create Grid
  2. 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.
  3. 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
  4. Set the grid style to “no fill” and style the outline.
  5. 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.
  6. Make a Key in your favorite vector tool. GIS software can’t help you now!

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Maps, conservation, insects, film, boats, scuba diving

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Andrew Middleton

Andrew Middleton

Maps, conservation, insects, film, boats, scuba diving

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