Remote Island Train Map

d3 Directional-Force Map

Challenges

• I had previously worked with d3 for simple plot graphs, pie charts, bar charts
• Had never worked with more advanced d3 implementations, including force charts
• Had not worked with SVG markers, defs, or hover effects

Process

• Was familiar with how d3 uses data to generate coordinates, so basic line-node graph was completed within 2-3 hours
• Refactored provided data into array of cities and a way to populate nodes and reference links for much cleaner and easier to read code
• Spent about 4 hours learning and attempting arrowhead markers on lines, and associating labels with them
  • Eventually refactored code to first generate svg groups that hold line and marker so that the fill/stroke colors could match
• Spent (mumble) hours on attempting shortest path implementation, reading about Dijkstra's algorithm, and experimenting with online d3 dijkstra examples
  • Was unable to get shortest paths working

Lessons Learned

d3 Force

• This was entirely new, so all implementation was an experiment
• Had a lot of fun digging through various source code of online examples
• Sometimes nodes showed and no lines! Sometimes lines showed and no nodes! Figuring out why helped me understand what Force was doing on a deeper level
• Some references used include:
  • Mike Bostock's Force documentation
  • Force directed graph example
  • sathomas's d3 force blocks

SVG

• SVG markers do not inherit line color. Refactored code generating connection lines as groups holding the line and marker to manipulate highlight color effect.
• Leveraged these groups to add line titles as hover tooltips showing distances
• Some resources used include:
  • markers
  • defs
  • Implementation of marker ends
  • D3.js arrowhead markers

Shortest Path

• Spent most of my time down a rabbit hole reading source code and attempting this stretch goal
• Was unable to crack Dijkstra's algorithm or get various examples online working with my implementation
• Some references used:
  • Demonstration of Dijkstra's shortest path algorithm
    • Was the most promising, ran into difficulties with generating an Adjacency Matrix
  • Dijkstra's algorithm in Javascript/D3
    • Only changes line color based on distance, doesn't actually return the shortest distance between nodes
  • Simple Dijkstra Implementation in JavaScript
    • Was using this example to develop a recursive shortest-path approach of my own when I realized I had used up all of my time!

Background image via unsplash