Zoom level

What are zoom levels?

Internet maps (e.g. Google Maps, Bing Maps) are not freely scalable, but offer maps to specific, predefined scales. They also use a coordinate system, where there is no uniform scale, but a different scale at every point on the map.

For these reasons, the specification of scales in this area is usually omitted. Instead, zoom levels are used, which correspond to the fixed, precalculated maps. In addition, these precalculated maps are stored in the form of many small graphic files of the same size ("tiles").

The following logic is used here: The total map, often the whole earth, corresponds to zoom level 0, and everything consists of only one tile.

The scale of each subsequent zoom level is twice the scale of the previous zoom level (or half the reciprocal of the scale). For example, if zoom level 5 has a scale of 1:18.000.000, zoom level 6 has a scale of 1:9.000.000. This results from the fact that in the following zoom level the map is constructed with twice as many tiles both side by side and below each other.

Zoom levels in easymap

When designing maps, which are used in easymap explorer are to be released, the scale-dependent visibilities should be aligned primarily to the zoom levels. For this purpose, the tooltip of the control window Scale ranges also displays the zoom level, provided the mouse is over a vertical line. This zoom level is compatible with the zoom levels used by the well-known Internet map providers (e.g. Google Maps, Bing Maps).

Conversion between zoom levels and scales

In the section Scales it has been pointed out that the scale of a map is not the same at every point (depending on the coordinate system). Therefore it is not possible to specify a fixed conversion between scales and zoom levels. easymap, however, calculates a suitable conversion based on the map section.