by David Crowther
Question:
Is it possible to see the Tile Levels in QGIS?
Answer:
By default the status bar in QGIS will show the current map scale – e.g. 1:100, 1000, 2500, 5000….
However, when working in a web mapping application you will be working with Map Tiles and so the world changes from scales to pre-set Map Tile Zoom Levels. Here is a an OpenStreetMap wiki on this topic:
https://wiki.openstreetmap.org/wiki/Zoom_levels
With an example table showing you the correlation between Map Tile Levels and Map Scales.
Map Tile Levels are common to us as we have our own WebGIS – MapThat – where the map zooms in and out using Zoom Levels as shown in the map window. For example UK wide is around Level 7…
…. and Street Level is level 18,19 and onwards.
It is often quite useful to know what is the best zoom level to use in a web map and in particular what zoom level should we auto hide a specific complex spatial layer. To do this you can install the QGIS plugin – Zoom Level.
From the Plugins tool search for the word ZOOM and then install the Zoom Level tool.
Once installed you will then have to tick to show the Zoom Tile Panel. To do this choose View > Panels and select the Tile Scale Panel.
Once the Tile Scale Panel has been added you will now have an additional set of information on the QGIS Status bar on the left near the Search tool.
The value will show you the Map Tile Level for the current Map Scale. For example, at street level this Tile Level is approximately 21. We can then use this to zoom in or out to see the most optimum Tile Levels to show complex spatial datasets and also our Basemaps. This will be very useful in a WebGIS e.g. MapThat as we can use those settings to auto turn our complex layers and Basemaps on or off.
Another example is to identify the best Tile level to set as the Startup view for a WebGIS. For example here is the Liverpool City Boundary and the Scale Tile Level shows us that Zoom Level 12 or 13 is the best option to use.