How Spectrum Renders Maps

For backgrounds maps, Spectrum will usually use the Map Tiling Service or a third party source such as Bing or OSM. 256 x 256 pixel map tiles are returned and in all these cases the tiles are cached server side and generally will perform well.

For business maps (uploaded by customers and shown in the legend) Spectrum renders data live and makes a series of 542x542 pixel map image requests for each map in the legend. For example, we have two maps each with two layers as shown below. A map group relates to one Named Map loaded into Spectrum Spatial.

Figure: Map Legend

Map images are placed adjacent to each other on the map window to complete the whole map. The images are placed overlapping by 15 pixels to ensure map symbols do not appear cropped at the edges. Below we see that 6 map requests are needed to fully cover the map window, which results in a total of 12 map requests (6 for “Conservation Map” and another 6 for “Spaces and Trees Map”).

Figure: Map Images

The use of browse caching mitigates the issue to some extent. Once a map image is returned it is cached locally in the users browser for 60 minutes hence as the user pans and zooms and returns to the same location the cached map image is used. However if more map groups are present then more requests are made. We have had cases where a customer has around 70 map groups. If all of these were turned on by the user in the legend, and they had not previously browsed any of them in their current session, Spectrum would make 420 requests to render the map.