The mapping procedure consits of an interpretation phase, a fieldwork phase , and a phase for analysing the fied data and map preparation.
The assumption in mapping with the help of remote sensing images is that areas that
look homogeneous in the image will have similar features on the ground. The interpretation
process consists of delineating areas that internally appear similar and at the
same time different from other areas. Making an interpretation from only one aerial
photograph or a small part of an image from a space-borne sensor seems quite simple.You have the overview of the entire area at all times and can easily compare one unit to
another and decide if they are the same or different. Working with many photographs
and also with several people will, in contrast, require a clear definition of the units to
be delineated.
Definition of units is based on what can be observed in the image. Different interpretation
units can be described according the interpretation elements. After establishing
what the features are on the ground, ‘interpretation elements can be constructed, from which an interpretation of features can be made. These features are again described in terms of interpretation elements. If knowledge of the area is lacking (not yet available), you could also begin your interpretation based only on interpretation elements
(see the figure in the example ). After fieldwork, it will become clear what the units actually represent on the ground.
Prior to the delineation of the units, a legend is constructed based on interpretation
elements. The legend can be presented in the form of a table in which each element
type is represented by a column.
Maps and inventories should reflect what is actually on the ground. Fieldwork / visits should,
therefore, be made to observe what is there in reality. Field visits for ground observation
are time-consuming and usually costly. Making observations everywhere in the
entire area to be mapped is likely to take too much time. For reasons of efficiency,
remote sensing data are used to extrapolate the results of a limited number of observations
over the entire area being studied.
The selection of sample locations is a crucial step for cost-effective mapping. We can
use the RS images to stratify the area. To do this, we make an preliminary interpretation
of the area to be mapped based on its interpretation elements. The interpretation
units are the strata to be sampled.
From the correlation between collected field data and the interpretation, the entire area
can be mapped in terms of what is on the ground.
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