Geospatial data has two main components - spatial data and attribute data. Spatial data describes the location and geometry of features on Earth's surface, which can be discrete (individually distinguishable) like points, lines, and areas, or continuous (existing between observations). Attribute data describes the characteristics of spatial features. There are two main models for representing spatial data - the vector data model uses x-y coordinates to represent point, line and area features, while the raster data model uses a grid of cells. Projection transforms spherical Earth coordinates like longitude and latitude to a plane coordinate system for mapping.

1. Geospatial Data
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Dhanya Senthil

2. Geospatial Data
• The location, also called geometry of shape , represents spatial data,
whereas the characteristics are attribute data.
• Spatial Data
• Spatial data describe the locations of spatial features , which may be
discrete or continuous.
• Discrete features are individually distinguishable features that do not
exist between observations.
• Discrete features include points , lines , and areas.

3. • Continuous features are features that exist spatially between
observations.
• A GIS represents these spatial features on the Earth’s surface as map
features on a plane surface.
• This transformation involves two main issues : the spatial reference
system and the data model.
• The locations of spatial features on the Earth’s surface are based on a
geographic coordinate system with longitude and latitude values,
where as the locations of map features are based on a plane coordinate
system with x – y – coordinates.
• Projection is the process that can transform the Earth’s spherical surface
to a plane surface and bridge the two spatial reference systems.

4. .(x1,y1)
.(x3,y3)
.(x2,y1)
The vector data model uses x y coordinates to represent point
features (a) and the raster data model uses cells in a grid to
represent point features(b)
a b

5. • The vector data model uses points and their x- y - coordinates to
construct spatial features of points , lines and areas. The raster data
model uses a grid and grid cells to represent the spatial variation of a
feature.
• The georelational data model uses a split system to store spatial data
and attribute data.
• Topology expresses explicitly the spatial relationships between features
such as two lines meeting perfectly at a point and a directed line having
an explicit left and right side.
• Users of ESRI software recognize coverage's as topological data, shape
files as non topological data, and geodatabases as with or without
topology.

6. • Composite features are built on simple features of points , lines and
polygons.
• The triangulated irregular network , which approximates the terrain with
a set of non overlapping triangles , is made of nodes and edges .
• The regions data model, which allows regions to overlap and to have
spatially disjoint components , is built on polygons.
• The dynamic segmentation model, which has a linear measure system ,
is built on top of linear features.

7. • Attribute Data
• Attribute data describe the characteristics of spatial features.
• For raster data ,each cell has a value that corresponds to the attribute of
the spatial feature at that location.
• A cell is tightly bound to its cell value.
• For vector data , the amount of attribute data to be associated with a
spatial feature can vary significantly.