Scale, Accuracy, and Resolution in a GIS
Scale indicates the relationship/ratio between the distance on map to the physical distance on earth. For example if scale is 1: then, 1cm on map is . Map scale refers to the relationship (or ratio) between distance on a map and the corresponding distance on the ground. For example, on a scale map. The scale of a map is the ratio of a distance on the map to the corresponding distance on the When scale varies noticeably, it can be accounted for as the scale factor. (Hardly surprising since this is the relation used to derive Mercator).
In cartography, maps and projections, the concept and application of scale is of fundamental importance. By definition, it is a factor — meaning it is something to multiply or divide — so whether "scale" or "factor" is the adjective the particular word pairing has no obvious meaning, except in a particular context: Every map or globe has a stated or unstated scale The map or globe scale is a ratio of distance on map or globe to corresponding distance on the ground or reality.
Either it has no units or its units reflect the map and ground units — miles per inch, km per cm, etc. It is variously called scale, map scale, principal scale, representational fraction, or nominal scale.
Every map or globe has a (stated or unstated) scale
I like that last one, nominal scale, because most maps have a single statement of its scale. Sadly, it is sometimes also called scale factor. 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.
What is Map Scale?
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.
- Scale (map)
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.
Map Scales & Units
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.
MAPS AND SCALES
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.
Data detail Data detail is a measure of how much information is stored for each feature.
The graphic scale is a bar chart or "ruler" that is drawn at the bottom of a topographic map. This is the scale that you should use when asked to measure distances on the map. Note that the zero mark is not located at the left end of the graphic scale.
You may measure distances by marking off the 2 end points on the edge of a sheet of paper and aligning the edge of the paper against the graphic scale make sure one of your marks is on the zero.
When converting a verbal scale to an R. That is the basic difference between these two types of map scales. Decide which ONE unit to convert to: