Someone asked me which GIS SDK to learn after ArcGIS. Here's my stack-rank — and the honest reason behind it. The ESRI ecosystem is deep, but it's one company's answer to every question. The open-source alternatives aren't trying to replace it. They're solving different problems, often better.
Below: each SDK doing something the others can't. MapLibre renders 3D building geometry from OpenStreetMap data. Deck.gl draws GPU-accelerated evacuation arcs across a city. Leaflet loads real Census boundary polygons without a server. All running in a single HTML file.
MapLibre GL JS
When Mapbox went closed-source in 2020, the community forked it into MapLibre. Today it's the dominant
open-source WebGL vector tile renderer — used by Felt, Stadia, AWS Location, and hundreds of orgs that
can't pay Mapbox pricing. The API is nearly identical to Mapbox GL JS.
What ArcGIS developers will recognize immediately: sources, layers, expressions, camera control, event
handling — all the same patterns. What's different: you're not locked to one tile provider, and the 3D
capability that ArcGIS SceneView requires a separate SDK for comes standard here. The map below is pitched
at 55 degrees, pulling live building geometry from OpenStreetMap, and rendering it in your browser with WebGL.
Deck.gl
In 2015, Uber's engineering team had a problem: millions of trip records, and nothing in the browser
that could visualize them at that scale. Leaflet froze. Everything else froze. So they built Deck.gl —
a rendering engine that hands the work to the GPU instead of the CPU — and open-sourced it.
The same tool built to show where rides were going in San Francisco now runs damage assessment maps,
displacement tracking, and resource positioning for humanitarian response worldwide.
The map below is fetching live data from the USGS earthquake feed — every earthquake recorded on Earth
in the past seven days. No synthetic data. No manual download. One API call, rendered instantly.
Size and color both map to magnitude. The Ring of Fire draws itself.
- →Load all shelters in your county — fast, no problem
- →Load all shelters in your state — starting to slow down
- →Load every 911 call from the past year — browser freezes
- →Try to pan or zoom while it loads — good luck
- →Every address point in a county — smooth
- →Ten years of incident data, all at once — smooth
- →Every parcel in a major city with live risk coloring — smooth
- →All of it updating in real time as you filter — still smooth
Leaflet
The most widely deployed web mapping library ever built — more websites run Leaflet than any other mapping
tool, and it's been that way since 2011. No WebGL, no GPU — it renders SVG and DOM elements. That's the
point. Leaflet is dead simple, has an enormous plugin ecosystem, and works on every device without exception.
The map below fetches real US state boundaries from the Census Bureau — actual GeoJSON, loaded at runtime,
styled as a FEMA-style risk choropleth. This is the pattern used by emergency managers in every county in
the country. Not glamorous. Extremely effective. Notice how little code it takes.
Cesium
A different category entirely. The three SDKs above are flat maps — even MapLibre's 3D buildings are
an illusion on a projected plane. Cesium is a true 3D globe: real WGS84 ellipsoid, real terrain elevation
from Cesium World Terrain, and photorealistic 3D tiles from Bing and Google. You can start in space
and fly down to street level without ever changing coordinate systems.
For disaster response, this matters when terrain is the story — flood inundation across a valley,
wildfire behavior on a ridge, helicopter routing around mountains. The globe below has flown to New Orleans,
tilted to show the terrain relationship with Lake Pontchartrain, with Cesium World Terrain active. Drag to
orbit. Scroll to zoom. Right-click drag to tilt.