Dijkstra Cartography
- All roads lead to my home (at least in Paris) [HD 14016x9599 / 7.3MB]
- The Amazon river / Rio Amazonas with all its tributaries [HD 11962x7625 / 3MB]
- Eastern European Railway (from Paris) [HD 29255x9624 / 10.8MB]
- World Flights (from Paris) [HD 17900x6600 / 17.72MB]
Introduction
I was fascinated by the project "Roads to Rome" by Moovellab but sad that it isn't opensource. Helped by this project (thanks @tristramg ) I started to build my own map.
I did not have any GIS background but it was very interesting to discover what we can do with. The code isn't very good (I'm not a C++ guru).
The project is named "Dijkstra Cartography" but sometimes BFS algorithm is better (if all the edges have the same weight).
This code can be useful for cartographer, as I found a lot of errors for the river Amazon (see here) or.. to have your own poster ?.
Extract
You may not want to use the planet.osm file (644GB - all the openstreetmap data in one file).
Choose the right file here and extract what you really need with openstreetmap's tools : osmconvert, osmfilter, osmosis, osmium...
One interesting way is that you can extract all the data within a polygon with osmconvert, and here are some cities polygons.
Routing, Map, Routing system used, -----------, ----------------------------------------------------------, Paris, Graphhopper - "Dijkstrabi", Amazon, Dijkstra's algorithm, Railway, OSRM, Flights, Dijkstra's algorithm
The first thing to do is to gather the statistics of usage of all paths :
for each location, execute the routing algorithm you chose to your root location (your home for example).
Merge all and sort the data by the most used path.
Projections, Map, Projection, -----------, -----------------------------------------------, Paris, Lambert 93-I EPSG:27571, Amazon, ESRI:102032 (South America Equidistant Conic), Railway, Mercator, Flights, WSG84, You can follow this guide, search SpatialReference or ESPG.io.
Drawing
Considering the data is sorted and well projected.
The width and height of the image are defined like this :
width = (maxX-minX)/scale;
height = (maxY-minY)/scale;
To draw these paths, I used this function (plotted using R) :
as it gives me a percent (between [0;1] here) of how the line width must be important. Also I can accentuate the decreasing by modifying parameters inside exp().
I used cairo and I was really suprised that I can understand these map without using any shapefile.
Details for each map
Bonus
