ArcGIS Server JSON to GeoJSON does not always work

ArcGIS Server JSON to GeoJSON: Why It Sometimes Just Won’t Play Nice

So, you’re trying to wrangle some data from ArcGIS Server into GeoJSON, huh? Join the club! It’s a task that sounds straightforward enough, but can quickly turn into a head-scratching exercise. We all love GeoJSON for its simplicity and how easily it plays with web maps. It’s the lingua franca of web mapping, really. But ArcGIS Server, bless its heart, often speaks a slightly different dialect – EsriJSON. And that’s where the fun begins.

Think of it like this: GeoJSON is that friend who’s super chill and just wants to get the job done, while EsriJSON is the overachiever who brings a spreadsheet and a PowerPoint presentation to a casual hangout. Both have their strengths, but getting them to communicate directly? That’s the tricky part.

Let’s break down why this conversion sometimes feels like pulling teeth.

First off, these formats just aren’t built the same. EsriJSON is like the deluxe model, packed with all sorts of bells and whistles to handle complex GIS data. GeoJSON, on the other hand, is more minimalist. It focuses on the essentials – simple features and their attributes. Trying to directly translate between these two can be like fitting a square peg in a round hole.

Then there’s the geometry. GeoJSON plays nice with your standard points, lines, and polygons. But EsriJSON? It might throw in some curveballs with extended geometry types that GeoJSON just doesn’t recognize. It’s like showing up to a baseball game with a cricket bat – technically a bat, but not quite the right tool.

Spatial references are another potential minefield. GeoJSON is all about WGS 84 (EPSG:4326) – the GPS standard. ArcGIS Server, however, can serve data in all sorts of coordinate systems. If you don’t handle that transformation properly, your data might end up plotted somewhere in the middle of the ocean. I’ve been there; trust me, it’s not fun. Pro tip: tack outSR=4326&f=geojson onto your URL and cross your fingers.

And let’s not forget about the sheer volume of data. GeoJSON, being text-based, can get pretty bulky, especially with large datasets. Imagine trying to load a phone book into your web browser – not exactly a smooth experience. I once tried to load a massive GeoJSON file of building footprints, and my browser nearly choked. Keep those files under 100 MB; you’ll thank me later.

Unicode characters can also throw a wrench in the works, especially if you’re using older versions of GDAL/OGR. And ArcGIS Server itself often limits the number of features it spits out per query. So, if you’re dealing with a huge dataset, you might only get a fraction of it, or the whole thing might just crash and burn.

So, what’s a GIS geek to do? Don’t despair! There are ways to make this conversion work.

The easiest route? If you’re using ArcGIS Server 10.4 or later, or ArcGIS Online, just ask for GeoJSON directly! Add f=geojson to your query URL, and you might just get lucky. Though, I’ve heard whispers that ArcGIS Online sometimes needs a little nudge to enable that export.

If that doesn’t work, it’s time to bring in the big guns: conversion tools. GDAL/OGR is your Swiss Army knife for GIS data wrangling. It can handle just about any format you throw at it, including ArcGIS Server JSON and GeoJSON. Just be aware that for newer versions of ArcGIS Server (10.3 and up), you might need to tweak some settings to get it to play nice.

Esri also offers some handy JavaScript libraries like Terraformer, which is specifically designed for converting between EsriJSON and GeoJSON. There’s also arcgis-to-geojson-utils, a more lightweight option if you just need the basic conversion. And if you’re using Leaflet, the esri-leaflet plugin has some built-in conversion methods.

You can also choose to do the conversion on the server-side or the client-side. Server-side conversion takes the load off the client’s browser, while client-side conversion gives you more flexibility to manipulate the data on the fly.

Dealing with a massive dataset? Break it down! Use the resultOffset and resultRecordCount parameters to grab the data in smaller chunks. Or, filter your query to only get the data you actually need. Tiling is another great option – it’s like serving your map as a bunch of little puzzle pieces, making it much easier to handle.

Whatever you do, make sure your coordinate systems are in order. And always, always, ALWAYS implement error handling. Trust me, you’ll save yourself a lot of headaches down the road. And once you’ve got your GeoJSON, validate it! There are plenty of online tools like geojsonlint that can help you make sure it’s up to snuff.

Finally, don’t be afraid to think outside the box. GeoJSON isn’t the only game in town. TopoJSON can give you smaller file sizes by encoding the topology of your data. And GeoPackage is a great option for storing geospatial data in a single, portable file.

Converting between ArcGIS Server JSON and GeoJSON can be a pain, no doubt about it. But with the right tools and techniques, you can tame that data and get it working for you. So, roll up your sleeves, dive in, and don’t be afraid to experiment. And remember, we’ve all been there!