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(GIS works on two types of Data - Spatial and Attribute
Data)
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Representing Spatial Elements
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Raster |
- Stores
images as rows and columns of numbers with a Digital
Value/Number (DN) for each cell.
- Units are
usually represented as square grid cells that are
uniform in size.
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Data
is classified as “continuous” (such as in
an image), or “thematic” (where each cell
denotes a feature type.
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Numerous data formats (TIFF, GIF, img etc)
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| Vector |
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Allows user to
specify specific spatial locations and assumes that
geographic space is continuous, not broken up into
discrete grid squares .
- We store
features as sets of X,Y coordinate pairs.
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We typically represent objects in space as three distinct
spatial elements:
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| Attribute |
•In
the raster data model, the cell value (Digital Number)
is the attribute.
Examples: brightness, landcover code, SST, etc.
•For
vector data, attribute records are linked to point, line
& polygon features.
Can store multiple attributes per feature.
Vector features are linked to attributes by a
unique feature number.
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| Raster
advantage |
- The most
common data format Easy to perform mathematical and
overlay operations.
- Satellite
information is easily incorporated .
- Better
represents “continuous”- type data.
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| Vector
Advantage |
- Accurate
positional information that is best for storing discrete
thematic features (e.g., roads, shorelines, sea-bed
features.
- Compact data
storage requirements.
- Can
associate unlimited numbers of attributes with specific
features.
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