How Historigraph works
A historigraph helps you understand history the way a map helps you understand geography. It is a map of time.
To understand the historigraph, you can compare it to other ways of visualizing change over time.
A timeline
Timelines frame history as a series of arbitrarily selected anecdotes whose relationships to one another must be inferred. They are only slightly better than a block of text at helping you understand how the world changed over time.
You also cannot zoom out very far to get the bigger picture because a timeline depends on readable text. To cover a long enough period in sufficient detail while keeping it all within your field of vision, the text would eventually have to become too small to read.
A line graph
A line graph is great for showing change in a single variable over time. But history is not a single variable. History is innumerable variables acting together and influencing one another.
You can show a few variables on the same graph. Add many more, and the graph quickly becomes visual chaos.
An animated map
A map conveys the state of the world at a particular moment. It captures a snapshot of complexity, but not the changes in that complexity that define history.
Animating the map adds time, but introduces another problem: your brain has a limited capacity to remember what it has just seen. Even comparing two moments means remembering what changed at every location between one frame and the next.
A series of maps
Displaying multiple versions of the same map at once lets you compare several snapshots in time and see how the world changed between them.
But you still have to repeatedly locate the same place across multiple maps. That consumes mental effort and limits how many places and moments you can compare at once.
How a historigraph works
Take a map of space
To make a historigraph, the first thing you do is select a geographic region. It could be a city, a country, a continent, or the whole world.
A map contains many spatial relationships. Each place has not only a distance from another place, but a position north, south, east, or west of it.
Project that map into a line
A map is a two-dimensional representation of a slice of the Earth. It has an X and Y axis. To make room for time, those two spatial axes must be condensed into one.
The challenge is to preserve as much of the map's spatial relationship information as possible. Otherwise, all you have is a random list of places.
Introduce time
Once the map has been projected onto a single vertical axis, an entire second axis becomes available. Use that axis to represent time.
Now space and time exist on the same graph.
Add data
Using color coding or heat mapping, the places arranged along the spatial axis can be quantified. Each cell represents a place at a particular moment in time.
The result is a graphic that can show patterns of change across both space and time at once.
That is a historigraph
A historigraph combines the spatial awareness of a map with the temporal awareness of a graph. Instead of showing where things are or how one variable changes over time, it shows how many places change through time together.