Geospatial Data

Learn about encoding geospatial data!

what are the two approaches of encoding geospatial data?

position as a visual variable follows geospatial position, or treat spatial position as abstract data

choropleth map what

encode the quantitative attribute as colour over geographic regions encoded as geographically accurate area marks

what are choropleth maps good for?

data that has been aggregated by location

problem with choropleth map 1

we want to map normalised data not raw data, size is not connected to data values

problem with choropleth map 2

colour and area variables are not separable

graduated symbol map

placing symbols on a map, visual variables of size, shape and colour can be used

problem with graduated symbol maps 1

overlap is a problem, with some symbols reacting worse than others

problem with graduated symbol maps 2

comparisons can be very difficult due to the lack of alignment

problem with graduated symbol maps 3

size can be a problem as symbols can get very small due to the actual data and become hard to decipher

problem with graduated symbol maps 4

conveying precise positions can be difficult. shapes that are used should spread evenly like a circle

cartogram

distort the shape of geographic regions so the size directly encodes the data attribute

dorling cartogram

geographic regions are represented as non-overlapping circles

flow maps

show movement or connections between locations through lines or arrows

how can additional data be encoded in flow maps?

line width, colour