Scale and Resolution

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In maps, scale and resolution are two commonly used terms. The size of scale and resolution determines the degree of detail of map elements to describe the actual features.

The map resolution mentioned in the field of GIS is also called Ground Resolution or Spatial Resolution Resolution, which represents the actual ground distance (meters) represented by a pixel on the screen.

Map scale refers to the ratio of the distance on the map to the actual distance on the ground. When calculating the map scale, the two parameters of ground resolution and screen resolution are usually used.

Screen resolution, also called pixel resolution, is often expressed in terms of the number of pixels per inch on the screen, that is, the Pixel per Inch, hence PPI (or DPI). The default screen resolution for general maps is 96. Pixel size is also used in some places to describe the resolvability of the screen, such as 0.28 mm in the WMTS standard.

The scale of the SuperMap is defined by the ground resolution and the screen resolution as follows:

Resolution: refers to map resolution and ground resolution, which is the actual ground distance (m) represented by a pixel.
PPI, the screen resolution, is the number of pixels per inch of screen length, which is 96 by default
0.0254 (m/inch) is the conversion of meters to inches

Finally, this formula can be abbreviated as: Scale = 0.0254/(Resolution*96).

You can use this formula to convert between scale and resolution. For example, the "wmts china" interface adopts the map classification specified in the "Electronic Map Data Specification for Geographic Information Public Service Platform", and the correspondence between the scale and ground resolution can be converted using this formula. See Add WMTS service interfaces for details.

The screen resolution (pixel/inch) is not specified in the WMTS 1.0.0 standard, but is defined by the pixel size (0.28mm = 0.00028m). The conversion relationship between the two is:

Screen resolution (PPI) = 1inch/ (pixel size (m)/0.0254 (m/inch))

For a WMTS 1.0.0 interface, the number of pixels per inch is: 1 inch/ (0.00028 m/0.0254 (m/inch)) = 0.0254/0. 00028 ≈ 90.714

The default value of screen resolution can be set by modifying the system configuration file of SuperMap iOObjects Java, that is, in %SuperMap iServer HOME%\support\objectisjava\bin\SuperMap.xml, set the following parameters to the desired values:

<CustomDPIX>96</CustomDPIX>
<CustomDPIY>96</CustomDPIY>

Note : In the products before SuperMap iServer Java 6R (2012) SP1, the screen resolution defaults to 76.2dpi.