177 lines
4.0 KiB
Markdown
177 lines
4.0 KiB
Markdown
# Mapping in JavaScript
|
|
|
|
---
|
|
|
|
## Today
|
|
|
|
- Discuss types of maps & appropriate library choices.
|
|
- Explore examples in D3, Leaflet, and MapLibreGL.
|
|
|
|
---
|
|
|
|
## Which Tool?
|
|
|
|
**What kind of map?**
|
|
|
|
|
|
|
|
Abstract/geometric representation of data.
|
|
|
|
D3 will provide the most flexibility & can use existing tools for color scales/interactivity/etc.
|
|
|
|
---
|
|
|
|
## Map w/ Cartographic Features
|
|
|
|
|
|
|
|
A different library will be necessary. Depending on needs **raster** or **vector** tiles.
|
|
|
|
---
|
|
|
|
## Choropleths in D3
|
|
|
|
<https://d3-graph-gallery.com/graph/choropleth_basic.html>
|
|
|
|
### Projection
|
|
|
|
<https://d3-graph-gallery.com/graph/backgroundmap_changeprojection.html>
|
|
|
|
---
|
|
|
|
## Leaflet and MapLibreGL Choropleths
|
|
|
|
- Projection choice constrained by tile layers.
|
|
- Need additional libraries (or pure JS) for interactivity & other graphics.
|
|
|
|
Demo/Tutorial: <https://leafletjs.com/examples/choropleth/>
|
|
|
|
---
|
|
|
|
## Base Maps
|
|
|
|
Instead of starting with a blank slate, it can be helpful to have a base map, but a base map is often comprised of many feature layers:
|
|
|
|
- Country/Ocean borders
|
|
- National Sub-divisions
|
|
- Roads
|
|
- Terrain
|
|
- Points of Interest
|
|
- ...
|
|
|
|
Drawing all of these layers adds up.
|
|
|
|
---
|
|
|
|
## Raster Tiles
|
|
|
|
An innovation that made web mapping scalable in the mid-2000s was pre-rendering base layers into image tiles.
|
|
|
|
|
|
|
|
---
|
|
|
|
## Raster Tiles
|
|
|
|
### Pros
|
|
|
|
- Simple to serve: just a lot of images.
|
|
- Each image at a zoom level ~approx same size.
|
|
- 100% consistent rendering.
|
|
- Any kind of imagery (watercolor, satellite maps, etc.)
|
|
- Minimal client-side processing needed.
|
|
- Good for dense data.
|
|
|
|
---
|
|
|
|
### Cons
|
|
|
|
- Fixed zoom levels and projection.
|
|
- Large file sizes for large Z.
|
|
- Need to create variants for all desired permutations of features.
|
|
- No modifications to styling after the fact.
|
|
|
|
---
|
|
|
|
## Vector Tiles
|
|
|
|
Instead of images, data is sent as images.
|
|
|
|
- Can create multiple variations per JSON, change road colors/etc without regenerating millions of images.
|
|
- Can be more efficient on bandwidth.
|
|
- Significantly more complexity on client and server side.
|
|
- Older devices may struggle to render them.
|
|
- Rendering relies on client library, can vary.
|
|
- Not suitable for dense data such as satellite imagery.
|
|
|
|
Blog Post from *today* on OSM switch to Vector tiles: <https://tech.marksblogg.com/osm-mvt-vector-tiles.html>
|
|
|
|
|
|
---
|
|
|
|
## Leaflet
|
|
|
|
**Raster Tiles w/ Vector Layer on Top**
|
|
|
|
<https://leafletjs.com/reference.html>
|
|
|
|
(Has plugins to use Vector Tiles via MapLibreGL)
|
|
|
|
---
|
|
|
|
## MapLibreGL
|
|
|
|
Vector-tile based library. Community fork of MapboxGL.
|
|
|
|
Mapbox is an innovator in the space, but also quite expensive.
|
|
|
|
MaplibreGL/MapboxGL are mostly compatible.
|
|
|
|
---
|
|
|
|
## General Workflow
|
|
|
|
- Use library to render map(s) to div(s) on page.
|
|
- Pick base layer, either raster or vector.
|
|
- If vector, possibly apply additional styling to base.
|
|
- Add additional vector layers based on your data & its features.
|
|
- Attach event handlers for interactivity on your features and/or input elements adjacent to the map.
|
|
|
|
---
|
|
|
|
## Pop-ups
|
|
|
|
Leaflet/MapLibre offer a simple API for adding pop-ups to features.
|
|
|
|
Reminder: hover/pop-up alone is **not enough interactivity** for final product.
|
|
|
|
---
|
|
|
|
## Examples
|
|
|
|
Leaflet & MapLibre examples
|
|
|
|
---
|
|
|
|
## Custom Base Layers
|
|
|
|
- [Stadia Maps Hosted Tiles](https://stadiamaps.com/products/map-tiles/), free for noncommercial/academic use. You will need an account though.
|
|
- [OpenMapTiles](https://openmaptiles.org/styles/) - free, meant for self hosting.
|
|
- [Mapbox](https://www.mapbox.com) - another paid solution, $$$.
|
|
|
|
---
|
|
|
|
## Other Libraries
|
|
|
|
- [Deck.gl](https://deck.gl) - Alternative renderer similar to Map*GL. TypeScript/React focused mostly, hard to use with JS we covered.
|
|
- [OpenLayers](https://openlayers.org) -
|
|
- [Cesium](https://cesium.com) - 3D-focused geospatial.
|
|
- Note: You can also get 3D rendering w/ D3 or MapLibreGL.
|
|
|
|
---
|
|
|
|
## More Examples
|
|
|
|
- <https://projects.fivethirtyeight.com/redistricting-maps/alabama/#Competitive>
|
|
- <https://projects.fivethirtyeight.com/partisan-gerrymandering-north-carolina/>
|