Compared to the other social studies course descriptions (CEDs), APHG’s CED provides a relatively thin backbone to guide our teachers through the school year. On the one hand, a thin outline gives teachers great flexibility to expand from its key terms, explore a particular topic in depth, or contextualize it locally for our students. The downside, of course, is that teachers coming into the world of geography for the first time might be unaware that there are many more ways to expand on course topics/terms that could strengthen a student’s understanding of course materials. 

I replay this revelation yearly, and across many parts of our course. But my first yearly encounter happens right away, at topic 1.1: IMP-1.A.1. “Types of maps include reference and thematic maps.” Leaving teachers to believe that there are two types of maps, and move on. 

I’ve always taught my classes about map types, something not explicitly stated in CED 1.1: Choropleth, Dot-density, symbol proportional, Isoline, Flow-Line, Cartograms, Cadastral, and heat maps. After all, they see these types of maps throughout the entire course. Frankly, I’m almost disappointed they are not mentioned. Perhaps this type of content would be the equivalent to AP Psychology’s Unit 0?

I can hear it now, “But if it’s not in the course description, then I don’t need to teach it…”

AHHHHHHHHHHhhhhhhhhh. 

Teachers then look for examples of thematic maps and name choropleth, isoline, cartogram, etc. as thematic maps – conflating them with map types, of which there is actually an important distinction.

Sometimes I find myself trying to get into the heads of the CED team and guess what the heck they intended to say when they wrote it – knowing full well how classroom teachers will interpret it.

• Did they mean for us to contrast these (Reference and Thematic)? 
• Expect us to expand on these and find examples on our own? 
• Is it written in some sort of important order/hierarchy? 
• Do they want me to show how these work together?

This week, when I re-taught this for at least the literal 100th time, it dawned on me that it was likely that last one. 

Where the CED Falls Short and Where You Can Expand

There are three distinct layers at work here, not two:

1. Reference map (base map): the underlying layer that gives us a reference for where.
2. Map type: the cartographic technique used to display data on top of that base. 
3. Theme / variable: the actual variable being mapped. 

And so, this is how I explained it to kids this week: “The reference map is the canvas, the map type is the medium, and the theme is the painting.”

Reference Maps: The Canvas Base Layer

Reference maps are general, all-purpose. They’re to help you locate and navigate, not to highlight spatial data patterns. Examples include:

• Political maps: boundaries, countries, states, cities.
• Physical maps: natural features like mountains, rivers, terrain.
• Topographic map: elevation and terrain detail.
• Road/street map: illustrating transportation lines and networks.
• Satellite imagery map: the actual photographed/sensed surface of the Earth.
• Nautical charts: water navigation: depths, coastlines, hazards.
• Aeronautical charts: air navigation: airspace, airports, flight paths.
• Cadastral maps: property/land ownership boundaries and parcels.
• General reference maps: combination of several features (roads, boundaries, water) without emphasizing one theme, like what you’d find in an atlas.

Map Types: The Mapping Technique

Map type refers strictly to the visual method used to represent data, not the variable itself. The seven that I typically make sure my students know include:

• Choropleth: shades formal regions (e.g. states, counties, parcels) by a data value.
• Isoline: connects points of equal value with lines (elevation, rainfall, ocean depth)
• Cartogram: distorts the size or shape of areas based on a data value rather than actual geography.
• Proportional symbol: places symbols, usually circles, sized according to a value.
• Dot-density: places one dot per unit of data, scattered within a region, to visually show density.
• Flow line: uses arrows or lines of varying width to show movement or volume between places.
• Heat map: uses color intensity or gradient to show concentration or density.

Thematic Maps: The Variable

The theme is the actual subject being represented, e.g. population density, GDP, migration flow, literacy rates, wildfire risk. A thematic map takes that variable and uses one of the map types above to relay it to the viewer in a way that’s most appropriate for the variable, effectively communicates spatial distributions, and is aesthetically pleasing.

Together, the three (Reference, Map Type, Thematic Map) are cartographic decisions that go into map making.

I put together a chart of examples below – Click through to see it better in Google Slides with links. You will notice that in some instances, the same reference map can pair with different map types depending on how the cartographer wants to display the data.

Bottom line, this is one of those moments where you can expand beyond the APHG CED to help your students get a clearer understanding of how reference and thematic maps work together to make beautiful spatial art. 

Have a great weekend.

H.I.