Slim down intro_graph

[tmcw]

After #3344, iD.min.js is 2mb. Not a terribly large bundle - not top priority to slim it down. But intro_graph.json takes up 25% of that size - 500kb without whitespace. Ideally we can reduce the size of intro_graph significantly.

[bhousel]

Yeah, I thought about this.. #1336 (comment)

I think it's mostly the river geometries that extend far beyond the parts of town where the tutorial happens.

Check out imagery.json - we can probably save some space there too..

[bhousel]

One weird but necessary thing rollup-plugin-json does is generate "gunky" output when importing json. (see rollup/rollup-plugin-json#5)

It creates a lot of extra keys -- but only the toplevel ones..

So instead of importing json with a lot of toplevel properties:

{'node1':{stuff}, 'node2':{stuff}, ... many more }
... then ...
import { default } from '../../../data/intro_graph.json';

...we get far less "gunk" in the generated bundle if we wrap each json file in a toplevel property:

{ 
  introGraphRaw: {'node1':{stuff}, 'node2':{stuff}, ... many more }
}
... then ...
import { introGraphRaw } from '../../../data/intro_graph.json';

This might be a good workaround for your issue rollup/rollup-plugin-json#11 too.

[bhousel]

Update on this: 2e81e71 gives us a handy function for exporting the intro graph. The tutorial is now a lot more open-ended, so it's easy to make whatever edits we want and save them to a new intro graph by calling id.history().toIntroGraph() in the developer console.

Using this trick, I trimmed back the rivers and simplified the admin boundary surrounding the city. I also removed a bunch of unnecessary area=yes and other things (see 9933a36). This slimmed the graph down from 527K minified to 293K minified. I'm going to leave the un minified file in source control, because it is easier for git to perform diffs that way, and rollup will minifiy it anyway when intro_graph.json gets bundled.

Next I'll add some more useful things to the intro graph per #3068, but probably not too much. I might also remove some more features from parts of the city further away from the tutorial. I guess the numbers can go up or down a little, but we have a lot more control over them now.

[iandees]

Starting with a pre-rolled graph like this makes me think that it might be good to add a short step to the walkthrough that reinforces the idea that it's OK to delete stuff that's obviously wrong. It might be a bit too complicated to describe all the caveats (the imagery might be old), but reminding people that they can both add and delete is an important thing.

[bhousel]

Yeah, good suggestion @iandees.. I was actually thinking of adding some "paper streets" somewhere in a farm field and having the user to delete them in the Lines chapter. Sound good?

[iandees]

Yea, that makes sense.