As any geospatial engineer will tell you, ensuring quick and easy access to geospatial data within web browsers and GIS software isn’t easy. Some of the datasets on koordinates.com and various Koordinates Enterprise sites are truly massive. Given that we want to get this data out to thousands of users, the way we choose to provide the data as maps to users — i.e. the technical standard we adopt — becomes incredibly important.
Better technical standards mean a better user experience. Simply put, we need a technical standard that enables rapid access across many users without demanding a ludicrous amount of server power, to ensure that data users can get the maps they need, when they need it. Ludicrous demands on server power are also ludicrously expensive for the data publisher (as you might imagine, this is something that we at Koordinates are looking to avoid!).
So, what are our options? While there are a range of technical standards used across the industry, there are only two open geospatial standards for displaying maps in applications, websites and GIS software, each with their own special acronym: WMS and WMTS.
Let’s start with WMS. This standard was developed way back in 1999. Without going into technical detail, WMS works by giving users a ‘screenshot’ of spatial data. This ‘screenshot’ has to be regenerated and reloaded every time a user repositions the map. When we’re talking about big maps with lots of layers, this adds up to a lot of reloading.
Why does this matter? First, the IT infrastructure costs to support a small number of users are very high. When we’re talking about delivering spatial data to all New Zealanders, this becomes uneconomic pretty quickly. Given that it can be hard to predict usage, planning future infrastructure costs is almost impossible. If an agency using WMS gets more users than it was expecting, then the quality of its service is going to drop dramatically.
Second, WMS is as awkward as hell. It doesn’t work with consumer mapping sites like Google Maps, and is slow and difficult for non-specialists to use. If you’re looking to get visualisations of your datasets seen by a lot of users, WMS isn’t the best choice. It will mean that people will find it harder to get and reuse the data; data release will also be a heap more expensive.
WMS was good for its day – but its day is rapidly passing. Currently, Koordinates deploys WMS only for small raster layers on LDS. If Koordinates used WMS for the large, popular layers on Koordinates.com, LRIS or LDS, we would never be able to cater for tens of thousands of users.
Luckily, we’ve come a long way since 1999. Google Maps, OpenStreetMap, Koordinates and other sites have since developed a better approach known as ’tiled maps’.
Tiled maps introduce two simple innovations. First, map loading in web browsers and GIS software happens much faster. Instead of sending users a big ‘screenshot’, tiled maps send a bunch of little map images. Viewed together, these images give users the map view they are after. This means that when you pan across the map – going, say, from Dunedin to Port Chalmers — you don’t need to wait for the entire map to reload, as you would under WMS. Instead, a tiled map simply adds new images to the section of the map already loaded. You can see this at work on Koordinates.com or Google Maps.
Second, tiled maps dramatically reduce IT infrastructure costs. Tiled maps pre-generate map images at a bunch of different zoom levels, which means you no longer have live servers generating ‘screenshots’ on demand.
To replace WMS in the future, we added support for the open tiled map standard WMTS, an OGC standard developed in 2011 that’s built on the success of sites like Google Maps.
If you check out the New Zealand SDI Cookbook, which provides guidance for the development of a national Spatial Data Infrastructure, you’ll note that it recommends WMS. This is because WMTS was in its infancy when the STI cookbook was being developed; as a result, it didn’t make the cut into the first version.
Since 2011, though, WMTS has found wider support, including in the latest releases of Esri’s ArcGIS. Unlike Google Maps, WMTS can be published in different map projections, including the standard NZ Transverse Mercator. This makes it a practical solution for the publication of online maps aimed at both professionals and general users.
So, in summary: WMTS is faster, it’s cheaper and it scales – which is precisely what we need for wider scale map release.