Performance & data compactness

Geo feature size

Complex geo features provided by base registries (like multi polygons) are often very accurate. Especially when querying feature collections, this results in very large response payloads eating up bandwidth and causing slow response times. For web applications, these payload sizes are unacceptable and will cause applications to become slow or unresponsive.

There are several solutions to overcome this issue:

Compression

Compression is an easy way to achieve reduction of the response payload size. While this will speed up the transfer of the data from the server to the client, the data still needs to be uncompressed and loaded into memory within the browser of app.

HTTP compression

HTTP compression is a capability that can be built into web servers and web clients to improve transfer speed and bandwidth utilization. The most common compression schemes include Gzip and Deflate.

Gzip is a (de-)compression utility using Lempel-Ziv coding (LZ77) and is broadly used by webservers like Apache and Nginx to compress response payloads without the risk of data loss.

In order to receive a gzip-encoded response the client must set an Accept-Encoding request header. Here is an example of a properly formed HTTP header for enabling Gzip compression:

Accept-Encoding: gzip

TopoJSON

TopoJSON is an extension of GeoJSON that encodes topology. Rather than representing geometries discretely, geometries in the TopoJSON format are stitched together from shared line segments called arcs. Arcs are sequences of points, while line strings and polygons are defined as sequences of arcs. Each arc is defined only once, but can be referenced several times by different shapes, thus reducing redundancy and decreasing the payload size.

Besides GeoJSON, TopoJSON supports other source formats like ESRI shapefiles and CSV. It is also capable of simplifying geo features, a topic we will cover in the next section. Similar to HTTP compression, TopoJSON needs to be decompressed before the data can be used. Since TopoJSON performs compression at another level than HTTP, these two compression methods can be used in conjunction to return the smallest payload possible.