|
![]() |
![]() |
![]() |
Scale
The definition of scale for graphic elements is the same for representations on the screen as well as for
representations on paper documents. Depending on the purpose of modeling, the modeling of reality is more
complex or more general. This fact influences the scale. Which objects should be represented? Which geometric
primitive should be chosen for a specific representation: Points, lines, polygons? Which generalization factor
should be chosen to design the contours? In the following, similar issues are discussed:
The scale corresponds to the degree of resolution in which the
phenomena or the environment are described. It's an inherent property of the observation. Elements with a
different precision can coexist in a spatial database. For example, the georeferencing of water hydrants
is very accurate (accuracy of cadastral maps, several centimeters), while forest boundaries are at a resolution
of few meters.
In the context of GIS it is essential to distinguish between modeling scale or observation
scale and scale of cartographic representation. The choice of a
scale depends on the modeling purpose. The purpose determines the presence and richness of spatial features which
are described as well as the amount of information which is referred to the objects. The scale of cartographic
representation is dictated by the technical, graphical, physical (capacity of the visual system) and aesthetic
constraints. In practice, there is a big interdependence between these two types of scale because the map is both,
a source of information about spatial elements as well as a product provided by GIS. One centimeter on a map at a
scale of 1:25'000 corresponds to 250m in reality, or to 1km on a map with the scale of 1:100'000. Have a look at
the examples below, the national maps extracted from the Federal Geo-Information center.
![]() |
How to evaluate the scale?A rule of thumb defines when an object becomes observable if represented on a cartographic document. It's reasonable to state that an area on the map, which is less than 1x1mm, can't be a zonal component. That's why the map scale is associated to the spatial resolution. It is recognized that a resolution of 10m for example corresponds to a spatial precision of the order of 1:10'000. This rule provides an order of magnitude which has to be exploited carefully. This rule is not valid for the display or the printout of digital images, as a fuzziness, unpleasant from a visual point of view, appears when the side of the pixel exceeds 0.3 to 0.4 mm. |
There are three maps with different spatial scales visible in the following.
Note and comment on the differences between the maps. Which scale would you choose to represent your environment if you were:
Comment on your choice.
Solution (Click here for more information)
![]() |
![]() |
![]() |
![]() |