• SPATIAL DATA MODELS
• DATA REPRESENTATION
• VECTOR DATA MODEL
• TYPES OF VECTOR DATA MODELS
• ADVANTAGES AND DISADVANTAGES
• A Geographic Information System (GIS) is a
system designed to capture, store, manipulate,
analyze, manage, and present all types of
• GIS involves HW/SW, databases and models,
people and processing for decision-making.
• The process is second stage in designing and
implementing a data model.
• At present there are two main approaches in
which computer can handle and display spatial
• They are the raster and vector approaches.
SPATIAL DATA MODELS
• The traditionally spatial data are stored in the form of digital databases
and presented them in the form of maps.
• Two basic types of spatial data models have been evolved for storing
geographic data digitally.
• These are referred to as
• GIS data represent real object which can be stored under broad type known as
raster data and vector data.
• Raster data is made up of a matrix of pixels (cells).
• The vector data is made up of points, polygons and lines.
• As compared to the vector data structure, the raster data structure is not
particularly accurate as representing discrete features that is, those feature that
have a distinct boundary and shape.
VECTOR DATA MODELS
The vector data models use points, their XY co-ordinates to construct
The vector data models represent geographic features similar to the
ways as maps do.
Points represent geographic features too small to be depicted as lines
or areas; lines represents geographic features too narrow to depict as
areas; and areas represents homogeneous geographic features.
TYPE OF VECTOR MODELS
• SPAGHETTI MODEL
This is the simplest vector model with one to one translation of the
graphical image on the map as the name suggests these vector files are
simple lines with arbitrary starting and ending points just like
following the path of the single stand of spaghetti through a pile of
spaghetti on one's plate.
PROPERTIES OF SPAGHETTI DATA MODEL
• Point is enclosed as single XY co-ordinate pair.
• Line is encoded as a string of XY co-ordinate pairs.
• Polygon is encoded as a closed loop of XY co-ordinates
that define its boundary.
• The Spaghetti model is a file of spatial data constructed
in this manner is essentially a collection of co-ordinate
strings with no inherent structure-hence the term
• Although all the spatial features are recorded the spatial
relationships between these features are not encoded.
TIN DATA MODEL
• The TIN model creates a network of triangles by storing
the topological relationships of the triangles.
• The fundamental building block of the TIN data is the node.
• Nodes are connected to their nearest neighbors by edges,
according to a set of rules. Left-right topology is associated
with the edges to identify adjacent triangles.
• The TIN creates triangles from a set of points called mass
points, which always become nodes. The user is not
responsible for selecting; all the nodes are added according
to a set of rules.
DIFFERENCE BETWEEN VECTOR AND
RASTER DATA MODEL
• Vector Data Model: [data models] A representation of the world using
points, lines, and polygons. Vector models are useful for storing data
that has discrete boundaries, such as country borders, land parcels,
• Raster Data Model: [data models] A representation of the world as a
surface divided into a regular grid of cells. Raster models are useful for
storing data that varies continuously, as in an aerial photograph, a
satellite image, a surface of chemical concentrations, or an elevation
• Both vector and raster data constitute of "latitudes and longitudes",
only. The difference is in the way they are displayed.
• Latitudes and Longitudes in Vector data are displayed in the form of
lines, points, etc.
• Latitudes and Longitudes in Raster data are displayed in the form of
closed shapes where each pixel has a particular latitude and longitude
associated with it.
ADVANTAGES OF VECTOR DATA
• Data can be represented its original resolution and form without
• Graphic output is usually more aesthetically pleasing (traditional
• Since most data, e.g. hard copy maps, is in vector form no data
conversion is required.
• Accurate geographic location of data is maintained.
DISADVANTAGES OF VECTOR DATA
The location of each vertex needs to be stored explicitly.
Algorithms for manipulative and analysis functions are complex and
may be processing intensive. Often, this inherently limits the
functionality for large data sets, e.g. a large number of features.
Continuous data, such as elevation data, is not effectively represented
in vector form. Usually substantial data generalization or interpolation
is required for these data layers.
Spatial analysis and filtering within polygons is impossible
• Vector formats are either page definition languages or preserve ground
Common vector formats are
• Hardware Specific Formats/ Plotter formats
• Digital Exchange Format (DXF)
• Digital Line Graph (DLG)
• SVG(Scalable Vector Graphics)
• Arc-Info Coverage
• Arc-Info Interchange (e00)
• A data model in Geographic Information Systems is a mathematical
construct for representing geographic objects .
• Integrated raster and vector processing capabilities are most desirable
and provide the greatest flexibility for data manipulation and
• In many respects, vector and raster data models complement each
other and get switched between along the processes of data collection,
observation, analyses, and presentation.
• Fundamentals of GIS(2007) by:Debashis Chakra borty-Rabi N.Sahoo-
• Remote sensing and G.I.S & Fundamentals of G.I.S (2000),M.Anji Reddy-
• Introduction to G.I.S by: Kang- Tsung Chang –PP:31-53,117-133
• G.I.S Basics (2008) by: Shahab fazal pp:155-203