4 - Central Institute of Brackishwater Aquaculture

National Workshop-cum-Training on Blolnformatics and Informatlon Management In Aquaculture
existing coverage but are on a new DOQ. Likewise, the method can be used for
editing a vegetation coverage based on new information from a new DOQ that
shows recent clear-cuts or burned areas. Obviously, the major shortcoming of
this method is the resolution of the computer monitor, which is much coarser
than a digitizing table or a scanner.
6.0 Data Storage in GIS
There are two major types of format in which data can be stored in a GIs. Ttie
vector format and the raster format
6.1 Vector Format: In vector models, objects are created by connecting points
with straight line (or arcs) and area is defined by sets of lines. Information about
points, lines and polygons is encoded and stored as a collection of x, y
coordinate. Location of a point feature such as tubewell can be described by a
single x, y coordinate. Linear feature such as river can be stored as a collection
of point coordinates. Polygon feature, such as river catchment can be stored as a
closed loop of coordinates. Vector models are very useful for describing discrete
features like data represented by an area. Vector model is not much useful for
describing continuously varying features such as soil type.
6.2 Raster Format: Raster format uses regularly spaced grid cells in specific
sequence. An element of the grid cell is called ,a pixel (picture cell). The
conventional sequence is row by row from the left to the right and then line-byline
from the top to bottom. Every location is given in two dimensional image
coordinates; pixel number and line number, which contain a single value of
attributes.
Fig. 1 Vector and Raster Formats
7.0 Questions GIs can answers
Till now GIs has been described in two ways:
1. Through formal definitions, and
2. Through technology's ability to carry out spatial operations, linking data
sets together.