How is the base map is merged to bike data?

[cgoldammer]

Hi! Thank you for providing both the webpage and the code, this is very useful. I am working on a related project and would love to re-use your work and of course I'd reference it and extend through PRs if sensible.

I've looked at the code and couldn't figure out how the map with all NYC streets and bike lanes is constructed. If I had to guess, it's already in this layer. But how is this layer constructed? I'm assuming the bike lane data is somehow merged to some data of NYC streets, but what is this merge process?

If I had to do it myself, my best guess is that I can use segment id values to merge, but any guidance would be appreciated. Thanks!