Unit8 GIS it is the course of the geographic information system

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UNIT 8 INTRODUCTION TO GIS
Structure
8.1 Introduction
8.2 Objectives
8.3 Definition of GIS
8.4 Components of GIS
8.5 History of GIS
8.6 Data Models in GIS
8.6.1 Vector Data Model
8.6.2 Raster Data Model
8.7 Vector Data Analysis
8.7.1 Data Acquisition
8.7.2 Data Query
8.7.3 Geoprocessing of Vector Data
8.8 Raster Based Analysis
8.8.1 Single Layer Analysis
8.8.2 Multi-layer Operation
8.9 Applications of GIS
8.10 Let Us Sum Up
8.11 Key Words
8.12 Suggested Further Reading/References
8.13 Answers to Check Your Progress
8.1 INTRODUCTION
Geographic Information System (GIS) is a research tool for working with
geographic information. Also it can be construed as a science and
technology. It is basically a computer based system which is capable of
data capture and preparation; data management; data manipulation and
analysis; and presentation of data. These operations and capabilities of GIS
is enabled by computer system, software, data, infrastructure and GIS users.
The application of GIS increased since 1970’s and presently, it has wide
application in diverse fields. GIS is based on data models viz. vector and
raster data model. In this unit, we would discuss the components of GIS,
data models in GIS, and vector and raster data analysis.
8.2 OBJECTIVES
After studying this unit, you should be able to:
z explain the components of GIS;
z classify different types of data model; and
z explain the vector data and raster data analysis.

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8.3 DEFINITION OF GIS
The acronym GIS stands for Geographical Information System. Since this
is amalgamation of many different fields, there is no one agreed upon
definition of GIS. One of the broadly accepted definition as given by National
Center of Geographic Information and Analysis is: “A GIS is a system of
hardware, software and procedure to facilitate management, manipulation,
analysis, modeling, representation and display of georeferenced data to solve
complex problems regarding planning and management of resources” (NCGIA,
1990).
If we consider individual word in GIS: Geographic defines the spatial location
(where in the world), Information describes (specificity of the location), and
system (integration of different information about different locations). So, it can
be said, GIS stores information about world as a collection of thematic layers
that can be connected through geography.
8.4 COMPONENTS OF GIS
There are five basic components of GIS.
1. Hardware: Hardware component consists of a computer, data storage,
and display.
2. Software: Software includes the tools for management, analysis, display
and dissemination of spatial data and spatial information. There exists
several GIS software such as TerrSet, ArcGIS (ArcView, ArcEditor, Arc/
Info) GeoMedia; MapInfo; ERDAS (imagery analysis), AUTOCAD MAP
(drafting and design) MicroImages; Manifold, GRASS; PCI; ENVI; ER
Mapper
3. Data: Data is fundamental requirement for any GIS system. It can be spatial
(geographical location) or tabular (non-spatial) data. GIS combines spatial
and non-spatial part of data through database management system (DBMS).
4. Method: For efficient working of a GIS system, one need to have
knowledge of how to utilize GIS technology. Methods involve how data
is acquired, stored, processed, analyzed and displayed in a GIS system.
5. People: People constitute technical personnel (e.g. GIS analyst, manager,
programmers) who design, maintain and use GIS.
8.5 HISTORY OF GIS
The concept of GIS was first officially introduced in early 1960s, and thereafter
it was further developed and came up as a discipline. A Canadian Geographer,
Roger Tomlinson is considered as pioneer of the field who coined the word
“GIS” and was the first to store, collate and analyze data on land usage in
Canada. Although concept and discipline of GIS evolved in 1960s, the first
application of spatial analysis was done long back in 1832 when Charles Picquet
generated a map of cholera outbreak across all the districts of Paris. Later,

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John Snow in 1854 used the same concept to depict Cholera outbreak in
London.
The evolution of GIS can be described in three phases:
1. Early experimentation (late 1960s to middle of 1980s): The focus was on
conceptual and theoretical development.
2. Take off phase (middle of 1980s to early 1990s): The focus was on
application and technology transfer. There was rapid software
development in this era.
3. Maturation and professional establishment (middle of 1990s to until
now): During this time period, the focus was on technology consolidation
and advancement.
8.6 DATA MODELS IN GIS
As we move from real world to geographical representation in a system,
there are two concepts one need to understand:
1. Entity: Things in the real world which we wish to represent in a digital
system (e.g. river, building, soil type etc.)
2. Features: Our representation of the entity in the system that include
both geometric information (spatial data) and descriptive information
(tabular/non-spatial data).
To move from entity to features in a system, we need to use data model.
Data model is a consistent way to define and represent spatial features
in a database and relationships among them.
There are two types of data model:
8.6.1 Vector Data Model
The vector data model uses points and associated coordinates (X and Y)
to represent vertices of spatial features. There are three fundamental types
of vector model that exist in GIS (Fig 8.1):
a. Point: Point is a zero-dimensional feature which is represented by a
single coordinate (X and Y). Example: location of well, building,
sample location and so forth.
b. Line: Line is a one-dimensional feature that constitute explicitly
connected points. Lines are used to describe linear feature such as road,
rail, stream, faults and so forth.
c. Polygon: Polygon is a two-dimensional feature that is created by
multiple lines that loop back to create closed feature. In polygon, first
coordinate pair (point) on the first line segment is same as the last
coordinate pair in the last line segment. Polygons are used to describe
any geographic feature which has area such as forest, administrative
boundaries (e.g., state, country), geological formations, lakes, etc.

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Introduction To GIS
Fig.8.1: Vector data model representing point, line and polygons
8.6.2 Raster Data Model
The raster data model consists of rows and columns of equally sized picture
elements called pixels interconnected to form a planar surface. With the
advancement in technology, you may have already seen raster image when
you take picture from digital camera. If you zoom in the picture on a
computer, at some point you will start seeing small squares: building block
of the image called pixels. These pixels are used to represent any
geographical feature such as building, forest, park and so on. The pixel
size determines the smallest geographical feature that can be seen in a raster
data. The pixel size is the length of the side of square picture element
(Fig.8.2). If length of square pixel is 1 m then any geographical feature
with size less than 1 square meter cannot be viewed in the raster data.
Fig.8.3 depicts the geographical features both in vector and raster data
model. It is possible to convert from raster to vector data model and vice
versa. Figure 8.4 depicts an example representing raster to vector and vector
to raster. The comparison between and advantages of data models are
presented in table 8.1 and table 8.2.
Fig. 8.2: Rater data model describing extent, pixel size (resolution).

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Fig.8.3: Data Model: Vector Data Model (left), Raster data model (right). Same
data is represented in vector and raster data model in the two graphics.
Fig. 8.4: Raster to vector (top), vector to raster (bottom)
Table 8.1: Comparison of Raster and vector data model

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Table 8.2: Advantages of the data models
Check Your Progress 1
Note: i) Use the space given below for your answers.
ii) Check your answers with those given at the end of the unit.
1. What are the components of GIS?
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2. What are the types of data model in GIS?
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3. What are the differences between the vector data model and raster
data model?
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8.7 VECTOR DATAANALYSIS
This section discusses steps for vector data analysis.
8.7.1 Data Acquisition
The first step is to get the vector data in the system. There are several
ways to get it.
z Digitization from image or other maps
z Field coordinate measurement: Using GPS to collect the data in the
field which will have both coordinates of location and related attributes
of the location.
z Importing through excel: Many times data are available in the report
such as incidences of malaria at different locations (x, y). Given the
information of location and number of cases, one can get this
information in the GIS system.
8.7.2 Data Query
Query is information extraction from the attributes (tabular information)
associated with geographical features or directly from the feature itself.
There are two types of queries:
a. Query based on attribute
b. Query based on location
a. Query based on attribute:
Query based on attribute extracts the information from the given table based
on certain condition. For example: How much area is of forest in a given
landscape? How many countries have population more than 1 billion? Such
information can be extracted from an attribute table associated with
geographical feature. These queries in GIS are done using Structured Query
Language (SQL). The result of the query is set of records that satisfy the
condition. These results can be used for further analysis. For example,
selected record can be exported to new table, statistics can be calculated
on selected table, new values can be assigned to the selected record or
report can be prepared on the basis of records selected.
b. Query based on location (spatial query):
Spatial query is used to understand the spatial relationship between features.
There are three fundamental types of spatial relationship:
z Intersection: Intersection as name suggests intersecting boundaries of
two features. For example: To find if any road crosses a particular
forest patch.
z Containment: This describes if a feature is contained in another
feature. For example: Finding if a road is inside a geological unit.
z Proximity: This describes closeness between the features. For example:
to find how many schools are there within 200 meters of river bank.

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8.7.3 Geoprocessing of Vector Data
Geoprocessing is the processing of geographical information through spatial
analysis by transforming the dataset. The geoprocessing can be done on
one dataset or multiple dataset depending on the types of analysis. There
are three classes of tools:
z Breaking features into smaller features (e.g. clip, intersect, union). This
requires use of more than one dataset.
z Aggregating features into larger features (e.g. dissolve, merge). This
is done on single dataset (dissolve) or combining dataset (merge).
z Creating new features through buffering (e.g. buffer). This is performed
on single dataset.
The analysis done by using more than one dataset is called overlay GIS
operation. This is one of the most important operation where spatial and
attribute information from multiple data are combined into a single dataset.
Union: Union combines features of two or more themes. The extent need
to be same for the union operation. The operation can only be done on
polygon dataset and not on line and point data. The result contains new
set of polygons obtained by breaking down features. For example: To
determine the different soil types in land parcels, we can use union between
soil type polygon dataset and a dataset containing boundary of land parcel.
Intersection: Intersection results in area that is common in both the dataset.
This operation can be carried out by overlaying polygon over polygon/line/
point. Output type will vary depending on the type of vector feature used:
Polygon intersected with polygon will result in a polygon output. However,
polygon intersected with line (point) will result in a line (point) output.
Clip: Clip geoprocessing operation is carried out to extract those features
from lines, polygons or point layer which fall within spatial extent of
another polygon layer. Example: to identify those flood plains which are
inside a district of a state.
Dissolve: Dissolve operation combines adjacent polygons to form one
polygon based on a predetermined attribute. For example: If there is land
parcel layer with boundaries representing different owners. One of the
attributes in the layer is of soil type. If interest is to combine land parcels
with respect to soil types, then we can use dissolve with the predefined
attribute “Soil Type”. This will combine adjacent polygons with same soil
type.
Merge: Merge operation requires more than one layer that is spatially
adjacent to each other. The two layers need to have same attribute to
combine them. For example, if there exist land use layer for two neighboring
districts, merge can be used to combine them as one layer.
Buffering: Buffering operation is carried out on a single dataset that could
be point, line or polygon feature. The operation creates zone (zones) of
specified width around input feature. Example: To identify the plant species
those are found within 5 km distance from road, one can use buffer
operation on road layer.

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All these geoprocessing operations can be combined to achieve a goal. To
demonstrate the geoprocessing operations that we have discussed, let us
assume a hypothetical situation, wherein an environmental scientist is
interested in finding areas that are near deer wintering areas and water
bodies but far from traffic for a region.
The data available with the researcher are:
1. polygon layer of deer wintering areas,
2. polygon layer for water bodies and
3. road layer (line feature).
One can use most of the geoprocessing operations just now learned in this
exercise. Below is the flowchart demonstrating the steps:
Fig. 8.5: Flow chart of the steps for finding suitable areas satisfying conditions
viz. near deer wintering areas and water bodies but far from traffic, as given
in the problem.
Note: i) Use the space below for you answers.
ii) Compare your answers with those given at the end of this unit.
1. What are the steps in vector data analysis?
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.............................................................................................................
.............................................................................................................
2. What are the significance of spatial query?
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3. Explain the geoprocessing operations like union, clip, dissolve, merge, and
buffering.
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8.8 RASTER BASED ANALYSIS
Similar to vector data based geoprocessing, there are number of geoprocessing
operations that can be performed on raster as well. The operations covered
here include single layer analysis and multiple layer analysis.
8.8.1 Single Layer Analysis
This kind of operation is carried out using only one raster layer. One of
the most common operation is reclassification or recoding. For example:
if environmental scientist is interested in finding how much area of a given
landscape falls under low, medium and high elevation. Given elevation
raster with each pixel representing elevation value ranging between 10 –
1000 m, this can be found out by reclassifying the raster. Let’s say, 10
– 30 meters falls under low elevation (code 1); 30-60 meters falls under
medium elevation (code 2) and above 60 meters falls under high elevation
(code 3). One can do the reclassification giving code of 1, 2 and 3 to
the pixel depending on the pixel values and calculate frequency statistics
of how many cells falls under which category. Since every raster has pixel
size as discussed before, one can multiply area of each pixel with the
frequency to find out total area under each elevation class.
8.8.2 Multi-layer Operation
Raster to raster and raster to vector operation falls under this category.
z Clipping: Similar to vector clipping, raster clipping can be done using
spatial extent of vector layer. Example: Given global elevation raster,
one may be interested in getting the layer for a small region say for
a district. This can be done by overlaying district boundary over
elevation raster and using clip operation.
z Multi-raster mathematical overlay: This type of operation require
all the raster to have same spatial extent and same pixel size. One
can do most of the arithmetic operation on set of raster like addition,
subtraction, multiplication, division and so on. Let’s say one is
interested in finding out change in vegetation over 10 years with given
two raster of 2000 and 2010. These two raster have pixel value
representing vegetation status say ranging between 0 and 1. 0 implies
no vegetation and 1 implies maximum vegetation with value between
implying medium status. By subtracting the two raster, one can see
if the vegetation status has changed and how it has changed. The
decrease or increase in vegetation correspond to negative or positive
value in the result.

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8.9 APPLICATIONS OF GIS
The GIS has diverse applications in the field of climate change. Indeed, block
4 of the course MEV 024 deals exclusively with application of Geoinformatics
in climate change. Nevertheless, the following are few areas, where GIS is playing
an important role.
z Land use/land cover application: Land cover means the physical
characteristics of landscape. Land use means the way land is used for.
For example: An environmental scientist may be interested in finding
out how change in land use activities is affecting habitat of certain
animal species.
z Disaster management: GIS play major role in disaster management.
We can use GIS to find areas that are more prone to natural or man-
made disasters.
z Natural resource management: GIS has been used widely for natural
resource management. A forester can use it for mapping and monitoring
forest status. Agriculture scientist can use it for assessing crop yield,
crop type, and pest infestation, etc. Similarly, GIS can be used to figure
out geographical distribution of water resources.
z Irrigation mapping: Crop production in an area is mainly dependent
on water availability. Again GIS can be used for managing proper
utilization of water.
8.10 LET US SUM UP
Geographic Information System (GIS) is “a computer system for capturing,
storing, querying, analyzing, and displaying geospatial data”. “Geographic”
in GIS stands for the spatial location. The geospatial data describe both
the locations, and characteristics of spatial features. The concept of GIS
was first officially introduced in early 1960s. However, the discipline saw
great strides in terms of technology development, GIS software, and diverse
applications. As it is a science and technology, it is used as research tool
for working with geographic information. In this unit, we have discussed
the components of GIS which include hardware, software, data, method,
and GIS users. Further, we have discussed the different types of data models
such as vector data model and raster data model; and also analysis of vector
data and raster data.
8.11 KEY WORDS
Attribute Data : Data that describe the characteristics of spatial
features.
Data Exploration : Data centres query and analysis.
Digitizing : The process of converting data from analog
to digital format.
Geospatial Data : Data that describe both the locations and
characteristics of spatial features on the Earth’s
surface.

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Overlay : A GIS operation that combines the geometrics
and attributes of the input layers to create the
output.
Raster Data Model : A spatial data model that uses a grid and cells
to represent the spatial variation of a feature.
Vector Data Model : A spatial data model that uses points and their
x, y coordinates to construct spatial features
of points, lines, and areas.
Vectorization : The process of converting raster lines into
vector lines through tracing.
8.12 SUGGESTED FURTHER READING/
REFERENCES
Bolstad P (2014) GIS fundamentals, 2nd ed. CRC Press.
Chang K (2014) Introduction to geographic information systems, 4th ed.
McGraw Hill Education pvt limited.
DeMers M (2009) Fundamentals of geographic information systems. Wiley,
Hoboken, New Jersey.
8.13 ANSWERS TO CHECK YOUR PROGRESS
1. Geographical Information System consist of the following five basic
components of GIS.
z Hardware: Hardware component consists of a computer, data
storage, and display.
z Software: Software includes the tools for management, analysis,
display and dissemination of spatial data and spatial information.
Examples are QGIS, ILWIS, GRASS, etc.
z Data: Data is the basic requirement for any GIS system. It can
be spatial (geographical location) or tabular (non-spatial) data. GIS
combines spatial and non-spatial part of data through database
management system (DBMS).
z Method: For efficient working of a GIS system, one need to have
knowledge of how to utilize GIS technology. Methods involve how
data is acquired, stored, processed, analyzed and displayed in a
GIS system.
z People: People constitute technical personnel (e.g. GIS analyst,
manager, programmers) who design, maintain and use GIS.
2. Data model is a consistent way to define and represent spatial features
in a database and relationships among them. There are two types of
data model viz. Vector and raster data model.

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z Vector Data Model: The vector data model uses points and
associated coordinates (X and Y) to represent vertices of spatial
features. There are three fundamental types of vector model that
exist in GIS viz. Point, line, and polygon.
z Raster data model: The raster data model consists of rows and
columns of equally sized picture elements called pixels
interconnected to form a planar surface. The building block of
the image called pixels. These pixels are used to represent any
geographical feature such as building, forest, park and so on. The
pixel size determines the smallest geographical feature that can
be seen in a raster data. The pixel size is the length of the side
of square picture element.
3. Raster data model though involve simple data structure, require large
storage space for most data sets. Analysis of raster data is easy for
continuous data and also simple for many layer combinations. It is
good for display of images but discrete features may show “stair-step
edges”.
On the other hand, vector data model are complex and require small
storage space for most data sets. The coordinate conversion is much
simpler. It is preferred for network analysis. It displays map-like, with
continuous curves more appropriately. However, it is poor for display
of images.
1. The vector data analysis involves data acquisition, data query, and
geoprocessing of vector data. Data acquisition refers to getting the
vector data in the system. It is made possible through digitization from
image or other maps; field coordinate measurements; and importing
through excel. As regards the data query, it is information extraction
from the attributes (tabular information) associated with geographical
features or directly from the feature itself. There are two types of
queries viz. query based on attribute, and query based on location.
Geoprocessing is the processing of geographical information through
spatial analysis by transforming the dataset.
2. Spatial query is used to understand the spatial relationship between
features. There are three fundamental types of spatial relationship
namely intersection, containment, and proximity. Intersection suggests
intersecting boundaries of two features. Containment describes if a
feature is contained in another feature. Proximity describes closeness
between the features.
3. Geoprocessing is the processing of geographical information through
spatial analysis by transforming the dataset. It involves many operations.
Union: Union combines features of two or more themes. The operation
can only be done on polygon dataset. The extent need to be same
for the union operation. The result contains new set of polygons
obtained by breaking down features.

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Introduction To GIS
Clip: Clip geoprocessing operation is carried out to extract those features
from lines, polygons or point layer which fall within spatial extent of another
polygon layer.
Dissolve: This operation combines adjacent polygons to form one
polygon based on a predetermined attribute.
Merge: Merge operation requires more than one layer that is spatially
adjacent to each other. The two layers need to have same attribute
to combine them.
Buffering: Buffering operation is carried out on a single dataset that
could be point, line or polygon feature. The operation creates zone
(zones) of specified width around input feature.

Unit8 GIS it is the course of the geographic information system

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