Change Analysis FAQs
How do you calculate change?
When there are two images of the same area
they are compared to look for differences. For a change detection,
one image is subtracted from the other to identify different pixels.
Corresponding pixels that have the same values in both years will
have a 0 when subtracted and indicate no change. Pixels with either
positive or negative numbers have changed.
The example above is a section of South Carolina from 1995 and
2000 and the change detection image is derived from the difference
between the images.
Return to Top
What does "change from" and "change to" mean?
When calculating change, an image changes from one land
cover type and changes to another. For example, if a forested
area was cleared and a housing development was built in its place,
the area's "change from" value is forest and the "change to" value
is low intensity developed.
Return to Top
What is a change matrix and how do you read it?
A change matrix is a table, similar to a spreadsheet,
that quantifies the amount of change that occurs between all of
the land cover types. The matrix shows the "From" classes as rows
and the "To" classes as columns. The number of rows and columns
is determined by the number of classes in the land cover image.
Each cell represents the area (in acres) of the land cover change.
In addition, the matrix can be used during data development to
identify changes that are unlikely to occur (e.g., high density
developed changed to a forest) for re-evaluation.
Return to Top
![[Skip Navigation]](/images/pixel.gif){kind=tracking}
