Cartographer's Toolkit

Over on twitter we’ve been compiling a list of isoline types. I started with this list:

• Isopleth/contour: Elevation
• Isogon: Wind direction
• Isotach: Wind velocity
• Isotherm: Heat, temperature
• Isograd: Geology

Others chimed in with the following:

• Isobar: Pressure
• Isoshear: Wind shear (and a whole lot more weather-related ones here)
• Isochrone: Travel time
• Isodistance: Travel distance
• Isopor: Change in magnetic declination

After all that fine collaborative work I found that Matt has provided us with a nice complete list already. But hey, reinventing the wheel is a great way to learn what wheels are all about. I think.

Anyway, reminding map makers about this type of data construction is a good thing. We aren’t seeing any isolines on interactive, digital maps these days. I only ever see them on static maps. (Prove me wrong.)

The mechanism for including them would be the same as any other dataset: create the data (use your GIS), then create a multi-level schema whereby more isolines are shown the more you zoom in. You can populate the map with more isolines with each subsequent zoom level by creating a scalerank or minscale field and populating that however you want and calling it in the code. You’d also need to label them with fairly wide halos–hoping that your background color is mostly uniform and using that background color for the halo color–to create a break in the line where the label is. Unless your software of choice has a built-in way of dealing with that.

Thanks @rsimmon, @vruba, @oeon, and @ungarjo for your input. And yeah, thanks @williamscraigm…isochalaz?!

I figured I’d try my own too…

Proven wrong! @smathermather has shown us this fine example of a multi-scale, digital map with contour lines, on the Cleveland Metroparks map. They’re visible once you zoom in to a high zoom level.