FLOOD06249

• County: Statewide
• Basin: Statewide
• Title: Introduction to GIS Concepts
• Date: 6/8/1994
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Since attribute data is linked to tabular data, you can perform various analyses on the data. For example, in
the query described earlier, you can impose thc condition that only those neighboring states of Virginia that
have a population in excess of 4.000,000 should be selected. The software would then select only the states
of Maryland, North Carolina, and Tennessee. in addition to Virginia.

Part 2: The difference between vector and raster data

Spatial data are usually represented using one of two data structures: Raster or Vector.

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Raster data are composed of an array of cells (usually square in shape).
The value of each cell represents the value of the feature. Each cell is
relerenced by a row and column number. In raster structures a point is
represented by a single grid cell; a line by a number of neighboring
. cells strung together, and an area (polygon) by a group of adjacent
cells. Image data, such as satellite imagery, is stored using this
structure. Each grid cell on the map is assigned a number. A color is
. assigned to each grid cell based on these numbers, Some GIS software
can use raster data only as a backdrop but there are others that provide
spatial analysis capabilities on raster images as well.
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