1.
OVERVIEW OF GIS
INTRODUCTION:
The resource managers, planners and decision-makers
depend on the information related to an area or location
for analyzing and implementing developmental plan.
Conventional data storage and management has failed
to satisfy their needs. With the advent of computers
technology the database management in term of
'where', 'what' has been classed through geographical
information system (GIS

2.
What is a Map ?
Maps are the main source of data for GIS.
What is a map?
A map is representation of the spherical surface of
the earth on the plain sheet of earth. In practice we
normally think of two types:
1. Topographic maps 2. Thematic maps

3.
Topogrpahic Map
A reference tool, showing the outlines of selected
natural and man-made features of the Earth.
It often acts as a frame to other information

4.
Thematic maps:
A tool to communicate, geographic concept such as
the distribution of population
densities, climate, soils, landmark etc.
Thematic maps are of two types
Chloropleth b) IsoPleth

5.
Types of Maps:
A Chloropleth map uses reporting zones as census
tracts to show data such as average incomes or soil
geology etc.
An IsoPleth maps shows an imaginary surface by
means of lines joining points of equal value "Isolates
(eg. Controls on a topographic map)

6.
Characterstics of Maps:
The general Characteristics of maps are
-Maps are often stylized, generalized required
careful interpretation
-Usually out of date
-Show only static situation
-Often highly elegant/artistic

7.
What is GIS?
GIS stands for geographic information system. GIS has been variously
defined as -
- "A spatial data handing system"(Marble etal.1980)
A computer assisted system for the capture, storage, retrieval, analysis and
display of spatial data with in a particular organization (Clark, 1986)
A set of tools for collection, storing retrieving at will , transforming and
displaying data from the real world for a particular set of purpose
(Borough, 1986)
continued…..

8.
What is GIS? - 2
An organized collection of hardware, software, geographic data, and
personnel designed to efficiently capture, store, update, analyze and
display all forms of geographical referenced information(ESRI) or simply A
computer system capable of holding and using data describing place on the
earth's surface
the last definition needs little elaboration which highlights the components
of a GIS are :-
Computer hardware
Software
Spatial data and their attributed and
Trained personnel

9.
Uses Of GIS
GIS does not function by itself and it must be
emphasized that a group of well-trained persons skilled
in the technology are crucial components are termed as
"Humanware". GIS can be used as a decision support
tools in solving increasingly complex urban and
environmental problems. Forestry and wild Life Tracking.
Waste Land Developments, Agriculture and Ground
Water Resource water resource Management. Urban
application include utilities management, site suitability
analysis and demographic studies

10.
What a GIS is not
A GIS is not simply a computer for making
maps, although it can create maps on different scales
and in different projections.
A GIS is an analytical tool. The major advantage of a
GIS is that it allows one to identify the spatial
relationship between maps features and the non-spatial
data.

11.
GIS is a spatial database
GIS is a spatial database that answers these:
Application (In a typical Agriculture applications)
Locations, what is at……? (what crop exits at particular location)
Conditions: where is it…..?(which locations satisfy certain conditions) the crop is
associated with what soil type or what is the rainfall and so on
Trends using temporal data ? Trends can be seen in two points of time (whether a
particular crop increases or decreases. Soils have been degraded/eroded or not?
etc.)
Pattern: what spatial pattern exists
The display of crop zone cover superimposed on village, markets, road networks, as
shown a definite pattern

12.
GIS- Models
Models: "what if" (The GIS analyst can get answer
to some assumptions and presumptions like what
will happen to crop cover (rice/wheat) production if
population is doubled or agriculture area reduced
by certain percentage and water holding capacity
reduces.

13.
Types of GIS
GIS package acts on two types of data models.
These are
Raster Data Model
Vector data Model
Based on the data model, GIS are called as Raster
based GIS and vector based GIS

14.
Raster Data Model
The Raster model divides the entire study area into a regular
grid of cells in specific sequence
the conventional sequence is row from the top left corner
each cell contain a single value
it is space filling since every location in the study area
correspondents to a cell in the Raster
one set of cells and associated values is a layer and
there may be many layers in a database, eg soil type,
elevation, land cover, etc

15.
Vector Data Model
The vector model reduces the entire study area into three
geographical identities - the point, the line and the area
every geographical phenomenon can in principle be represented by
a point, line or area plus a label saying "what it is". The label could
be the actual be the names, or they could be numbers that cross-
reference with a legend, or they could be a special symbol
a map is a set of points, lines and area that are defined both by their
location in space with reference to a coordinate system and by their
non spatial attributes
vector objects do not necessarily fill space

16.
GIS software
Based on these two data models there are different GIS
software packages available in the market. Among these
ERDAS, IDRISI, SPANS ILWIS, MAP INFO and
ARC/INFO etc are the most popular ones, amongst
these ERDAS, IDRISI, ILWIS AND SPAN are Raster
based and Map info, ISRGIS and ARC/INFO are vector
based GIS software

17.
GIS compared to maps-1
Data Stores
Spatial data stored in digital format in a GIS allows for rapid access for
traditional as well as innovative purposes
Maps can be designed to be easy to convert to digital from e.g. by the
use of different colors which have district signatures when scanned by
electronic searching

18.
GIS compared to maps- 2
Data Indexes
This function can be performed much better by a good GIS due to the
ability to provide multiple and efficient cross-referencing and searching

19.
GIS compared to maps- 3
Data Analysis Tool
GIS is a powerful tool for map analysis
Traditional impediments to the accurate and rapid measurement of
area or to map overly no longer exists
Many new techniques in spatial analysis are becoming available

20.
GIS compared to maps- 4
Data Display Tools
Electronic display offers significant advantage over the paper map
Ability to browse across an area without interruption by map sheet
boundaries
Ability to zoom and change scale freely
Display in "3 dimensions" with "real time" rotation of view angle
Potential for continuo scales of intensity and the use of color and
shading independent of the constraints of the printing
process, ability to change as required for interpretation.

21.
Data Input
Data input is a process of converting analog data (map features) into a
digital form to develop a spatial database for further analysis required for
different applications. Data input is carried out through the process called
Digitization.
Input data to the GIS can come from several source such as digitized maps
from the output of digitizing table; Scanned maps from a scanner; ASCII
files containing point data with associated coordinated from GPS(Global
Positioning Systems) Surveys; text data from published sources such as
Census departments; Thematic maps from Satellite imagery etc.