A Question of Scale, Resolution, and MMU | Esri Insider
Scale. The image scale or map scale as it is sometime called refers to the relative difference in size or distance between the image and the. Because GIS data is stored in a very different way than paper map data, the relationships between map scale, data accuracy, resolution, and density are different. If you have used any raster data to make maps you may have at one time or another asked yourself, “What is the appropriate resolution of raster.
For example, if your map showed the whole of Europe, you would not want to see every single street, as that would cause urban areas to be so densely crowded with streets that the map would essentially be unreadable. In the digital environment, you see one map for all of Europe and the number of features that are drawn changes, with more features drawn as you zoom in. This is accomplished by the cartographer setting up multiple maps and multiple rules about what gets drawn when and at what color and line width and what gets labeled.
As a digital cartographer, one of the critical jobs is making sure the map is used at the correct scale.
On map scale and raster resolution
The cartographer can no longer rely on the medium paper previously and web now to control access and must consider how the map is experienced. For example if the road data shown came from a map at 1: Resolution With maps, resolution generally means one of two things. Raster data is unique in spatial data as it has a visible measure of how precise the data is: When a raster is created, it is a fixed set of rows and columns, and each cell in this set is a fixed size.
That fixed size is the resolution of the data. With raster data, that cell is often referred to as a pixel. The map uses symbology applied to these values to draw the raster. An example of imagery is that from Landsat—its raster data can have a 15m resolution each cell in the rows and columns is 15m x 15m in size. Resolution is based on the sensor or the technique used to create the raster. It is important to recognize that rasters can be processed and their cell size changed, this does not change the resolution.
For example Landsat imagery has a 15m resolution, you could process the data and change the cell size to 5 m, but the resolution of the data is still 15m. Example of raster resolution using Landsat 15m imagery. Example of raster resolution with 30m DEM.
Resolution and Scale
How far away is a map feature from its actual location in the world? This last, or 'locational' accuracy is of interest here, and is generally stated in terms of uncertainty. A rigorous statement of accuracy will include statistical measures of uncertainty and variation, as well as how and when the information was collected. Spatial data accuracy is independent of map scale and display scale, and should be stated in ground measurement units.
Data resolution Data resolution is the smallest difference between adjacent positions that can be recorded.
Since a paper map is always the same size, its data resolution is tied to its scale. Resolution also limits the minimum size of feature that can be stored. Therefore, on a 1: This resolution is far greater than the uncertainty of any of BC Environment's data. Raster data resolution Raster data is stored as usually square pixels, which form a grid or mesh over an area of the earth.
The size of these pixels determines the resolution of the raster, because it is impossible to store anything which falls 'between' the pixels. A GIS allows raster pixels to be any size, although they should not be smaller than the uncertainty of the data. If a raster coverage is derived from vector linework, its pixels should not be smaller than the uncertainty in the linework. If it comes from an air-photo or satellite image, its pixels should not be smaller than the resolution of the camera that recorded it.
Data density Data density is a measure of how many features per area are stored, and may imply a minimum feature size. Greater density implies more features in a given area, and therefore the features may be smaller. The density of paper map's data is limited by its scale and therefore its resolution. Areas polygons cannot be shown if they are smaller than the lines which draw them. For example, a polygon less than metres wide cannot be drawn on a 1: This minimum size also limits the number of polygons that can be represented in a given area of a paper map.
A GIS stores its data digitally, so the minimum size of a feature is limited only by the resolution, which is effectively infinitesimal. Where the degree of detail in a coverage is arbitrary eg soil polygonsa data definition or convention should specify the minimum size of features, and therefore their density.
Without this, different parts of the same coverage may have widely varying degrees of detail, influencing analysis results.
On map scale and raster resolution
For the same map, the scale is unique. The scale and the resolution are two different expression ways. So they are one to one. The conversion formula between scale and resolution is as follows: The number of pixels per inch.
As the scale and resolution is one to one, the scale is determined by latitude and zoom level and is related to PPI. Take googlemap for example, when the map is full extent and panning the map up and down, the latitude of the map center line will change and the scale will change, too. Similarly, when the map is in different zoom levels, the map scale will change, too. It is as shown in figure1 and figure 2, the change of latitude and the zoom level leads to the change of the scale.
The scale in view refers to the scale of the center. Compared figure 3 with figure 4, the map scale does not change when panning the map up and down. The latitude change is very small when the zoom level is very large, i. So the scale is basically the same. Scale-related attributes of Map and Layer are recommended. Because SuperMap server directly supplies scale functions of related maps. If the server does not directly supply scale, or standard services like WMS does not supply the scale parameter, the resolution attribute such as Resolution, Resolutions, etc is recommended.