This document provides an overview of geographic information systems (GIS). It defines GIS as software that can acquire, store, retrieve, and analyze spatial and non-spatial data describing physical objects on Earth. The document discusses the history of GIS, common software packages, data structures and management, and basic GIS operations such as data access, analysis through overlaying layers, and map production.

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GEOGRAPHIC INFORMA TION SYSTEM
GEOGRAPHIC INFORMA TION SYSTEM
1..Starter…………………………………………………………………………………………....3
1 Starter………………………………………………………………………………………… .. 3
2..GIS defiiniitiion………………………………………………………………………………..…..3
2 GIS def n t on……………………………………………………………………………… … 3
3..GIS Hiistory………………………………………………………………………………………5
3 GIS H story………………………………………………………………………………………5
4.. Softwares…………………………… ………………………………………………………….5
4 Softwares……………………………
4..1.. MAPINFO Professiionall v 6..5………………………………………………………... 5
4 1 MAPINFO Profess ona v 6 5……………………………………………………… . 5
4..2.. ARC GIS…………………………………………………………………………………... 6
4 2 ARC GIS………………………………………………………………………………… . 6
5.. Data Structures iin GIS ………………………………………………………………………6
5 Data Structures n GIS ………………………………………………………………………6
6.. Data management requiirements of GIS………………………………………………... 8
6 Data management requ rements of GIS……………………………………………… . 8
6..1 Data modelliing and representatiion……..………………………………………….. 8
6 1 Data mode ng and representat on…… ………………………………………… 8
6..2 Data base management and anallysiis……………………………………………...11
6 2 Data base management and ana ys s…………………………………………… .1 1
6..3 Data Integratiion………………………………………………………………………..11
6 3 Data Integrat on……………………………………………………………………… 11
6..4 Data capture……………………………………………………………………………...11
6 4 Data capture…………………………………………………………………………… .1 1
7 GIS data operatiions………………………………………………………………………….. 11
7 GIS data operat ons………………………………………………………………………… 11
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1.Starter
Originally the purpose of maps was for navigation only because explorers and traders
wanted to know how to travel from one place to another through uncharted waters or over
unexplored lands. Later, after the invention of paper and as the science of cartography
advanced, people became interested in studying the relationships between natural and
manmade features on the Earth's surface. Recently, the demand for maps of the
topography and specific themes of the earth's surface, such as natural resources, has
accelerated greatly.
Scientists wanted to study man's use of the land, which led to the study of spatial
distributions of such things as soil, people, vegetation, climate, etc. First an inventory had to
be taken via which data was collected and recorded. Due to the large volume of data and
lack of mathematical tools qualitative methods of classification and mapping were used
initially. With the development of appropriate mathematical tools and the availability of the
digital computer spatial analysis and quantitative thematic mapping have mushroomed.
Before computers the spatial database was a drawing on a piece of paper or film. Various
symbols, colors and text codes together with legends were used to display geographical
entities. Other additional information was given in accompanying narratives.
Because the paper map was the spatial database the information it contained had to be
compromised, namely:
1. data volume was greatly reduced => local detail lost
2. map drawn extremely accurately and presentation clear
The collection and compilation of data and the publication of a printed map is costly and
time-consuming. To extract a single theme from a general-purpose map by hand is very
expensive. The need for information about how the earth's surface is changing annually,
monthly, weekly, daily, and even hourly makes conventional mapping techniques
inadequate and simply impossible by hand.
GIS is the mapping tool, which forms a marriage between remote sensing, earthbound
survey, and cartography. Be aware that computer-aided design drawing software can create
theme, display and print geo referenced data just like a GIS software package but that no
topology is present to permit spatial analyses to be performed.
2.GIS definition
The definition of GIS states that it is software, which can acquire, store, retrieve, and
analyze information describing physical properties of the geographical world. The scope of
GIS is for two types of data:
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(1) spatial data that includes maps, digital images, administrative and political
boundaries such as roads; transportation networks, physical data such as rivers; soil-
characteristics; climatic regions; land elevations.
(2) non-spatial data, such as census counts, economic data, and sales or marketing
information
Following figure encapsulates these data:
A GIS is designed to allow a user to ask an almost unlimited number of spatial questions as
follows:
* Where is object A?
* Where is A in relation to place B?
* How many occurrences of type A are there within a distance D of B?
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* What is the value of function Z at position X?
* How large is B (area, perimeter, and inclusion count)?
* What is the result of intersecting various kinds of spatial data?
* What is the path of least cost, resistance, or distance along the ground from X to Y
along pathway P?
* What is at points X1, X2,...?
* What objects are next to objects having certain combinations of attributes?
3.GIS History
The father of GIS is recognized to be Dr. Ian McArth, a landscape designer, who published a
book in 1969 dealing with spatial representations of features in 2 and 3 dimensions. In the
1970s Dana Tomlin, a Ph.D. student at the Harvard Graphics Lab, developed the first raster
GIS program called MAP. This software was in the public domain so others developed it
further. These individuals were Dr. Duane F. Marble, Dept. of Geography, The Ohio State
University, Columbus OH who developed OSU MAP-for-the-PC in the 1980s and Dr. Joseph
Berry, Berry & Associates, Ft. Collins CO. who developed PMAP. The 1980s saw a great
profileration of start-up GIS companies but in the last five years many have disappeared
such as PAMAP from Victoria, B.C. and SPANS from Ottawa, Canada. One of these
companies, Environmental Systems Research Institute (ESRI), Redlands, CA under the
leadership of Dr. Jack Dangermond, developed the concept of linking attributes stored in a
database to map features in 1984. This simple idea revolutionized the GIS industry. At
present ESRI has captured about 90 percent of the GIS user community and has clients all
over the world. However there are still others GIS software vendors that are alive and doing
well such as MAPINFO, MGA from Intergraph, IDRISI from Clark University, ArcView GIS
to name a few.
4. Softwares
Following are two popular softwares:
4..1.. MAPINFO Professiionall v 6..5
4 1 MAPINFO Profess ona v 6 5
With MAPINFO you can display data as points, as thematically shaded regions, as pie or bar
charts, as districts, etc. You can perform geographic operations such as redistricting,
combining and splitting geographic objects, and buffering. From MAPINFO you can perform
data powerful SQL queries and remotely access your data. For instance, it calculates
distances between customers and stores, compute which branch stores are the closest to
your biggest customers and color-code store symbols by sales volume.
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4..2.. ARC GIS
4 2 ARC GIS
ArcGIS is the collective name for three products - ArcView, ArcEditor, and ArcInfo. These
products are built on a common interface and core capability with each product offering a
different level of functionality. The basic building blocks of ArcGIS are:
* ArcMap - for displaying and querying maps
* ArcCatalog - for managing geographic data
* ArcToolbox - for setting map projections and converting data
a. ArcMap
In ArcMap, you make maps from layers of spatial data, choose colors and symbols, query
attributes, analyze spatial relationships, and design map layouts. The ArcMap interface
contains a list (or table of contents) of the layers in the map, a display area for viewing the
map, and menus and tools for working with the map.
b. ArcCatalog
Spatial data can be browsed on your computer's hard disk, on a network or on the Internet.
You can search for spatial data, review it, and add it as layers to ArcMap. ArcCatalog has
tools for creating and viewing metadata (information about spatial data such as who created
it and when, its intended use, its accuracy, etc.). ArcCatalog manages spatial data that
come in a variety of formats. The geodatabase is a new spatial data format designed
specifically for ArcGIS.
c. ArcToolbox
With this ArcGIS building block spatial data can be converted from one format to another
using a set of tools. Most tools have a wizard interface that walks you through each step of
a task. Also the map projection of data can be changed. About fifty map projections are in
common use. Over 300 different models exist (and are recognized by ArcMap) to describe
the exact shape of the earth. There are 36 commonly used tools for data conversion and
management in ArcToolbox for ArcView and ArcEditor
5. Data Structures in GIS
All geographical data can be reduced to 3 basic topological concepts -- the point, the line,
and the area. A label is also needed to identify what the entity is, e.g. a section of railroad
line could be represented by a line consisting of a starting and ending x, y coordinate and
the label "railroad".
A map is a set of points, lines, and areas that are defined both by their location in space
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with reference to a coordinate system and by their non-spatial attributes.
The map legend is the key linking non-spatial attributes to the spatial entities. Colors,
symbols and shading are employed to visually display non-spatial information.
Map data is stored in a computer in the form of files, which must be accessed and cross-
referenced quickly. Therefore, the organization of the data elements comprising such files is
very important. Database management systems (software) are used to control data input,
output, storage, and retrieval.
Consider the example of simple map M with two polygons labelled I and II shown below,
with the corresponding data structure.
Simple map M with two polygons I and II
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From the above data structure we have the following:
6. Data management requirements of GIS
6.1 Data modeling and representation:
GIS data can be represented in two formats:
* Vector
* Raster
A. The Vector View of the World
A vector based system displays graphical data as points, lines or curves, or areas with
attributes. Cartesian coordinates (i.e., x and y) and computational algorithms of the
coordinates define points in a vector system. Lines or arcs are a series of ordered points.
Areas or polygons are also stored as ordered lists of points, but by making the beginning
and end points the same node the shape is closed and defined. Topological models define
the connectivity of vector based systems. Vector systems are capable of very high resolution
(less than or equal to .001 inch) and graphical output is similar to hand-drawn maps. This
system works well with azimuths, distances, and points, but it requires complex data
structures and is less compatible with remote sensing data. Vector data requires less
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computer storage space and maintaining topological relationships is easier in this system.
Digital line graphs (DLG) and TIGER files are examples of vector format.
B. The Raster View of the World
A raster-based system displays, locates, and stores graphical data by using a matrix or grid
of cells. A unique reference coordinate represents each pixel either at a corner or the
centroid. In turn each cell or pixel has discrete attribute data assigned to it. Raster data
resolution is dependent on the pixel or grid size and may vary from sub-meter to many
kilometers. Because these data are two-dimensional, GISs store various informations such
as forest cover, soil type, land use, wetland habitat, or other data in different layers. Layers
are functionally related map features. Generally, raster data requires less processing than
vector data, but it consumes more computer storage space. Scanning remote sensors on
satellites store data in raster format. Digital terrain models (DTM) and digital elevation
models (DEM) are examples of raster data.
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C. Graphical Comparison of Raster and Vector Systems
It is important to stress that any given real world situation can be represented in both raster
and vector modes, the choice is up to the user. Each of these systems of representation has
its advantages and disadvantages:
Method Advantages Disadvantages
§ Requires greater storage space on
computer
§ Simple data structure
§ Depending on pixel size, graphical output
§ Compatible with remotely
may be less pleasing
Raster sensed or scanned data
§ Projection transformations are more
§ Simple spatial analysis
difficult
procedures
§ More difficult to represent topological
relationships
§ Requires less disk storage space § More complex data structure Not as
§ Topological relationships are compatible with remotely sensed data
readily § Software and hardware are often more
Vector
§ maintained Graphical output expensive
more closely resembles hand- § Some spatial analysis procedures may be
drawn maps more difficult
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6.2 Data base management and analysis
Data base management and analysis include the data characteristics and analysis
techniques required for each application. Data base requirements include data acquisition
costs, manipulation costs, data quality, data scales, and data base size. Data analysis
techniques are the functional capabilities of the software and hardware, which impact
system configurations.
Data base requirements can vary widely depending on the scope of the application; eco-
system, individual refuge, state, etc. The type of data also impacts the size of the files.
GIS data undergoes various types of analysis. For example, in applications such as soil
erosion studies, environmental impact studies etc.
6.3 Data Integration
GIS must integrate both vector and raster data from a variety of sources. Some times edges
and regions are inferred from a raster image to form a vector model, or conversely, raster
images such as aerial photographs are used to update vector models.
6.4 Data capture
The spatial representations of data set are most commonly stored as either vector features
or as raster data sets along with traditional tabular attributes. For example, an RDBMS table
can be used to store a feature collection where each row in the table represents a feature. A
shape column in each row is used to hold the geometry or shape of the feature. The shape
column holding the geometry is typically one of two column types:
· A binary large object (BLOB) column type
· A spatial column type
A homogenous collection of common features, each having the same spatial representation,
such as a point, line, or polygon, and a common set of attribute columns is referred to as a
feature class and is managed in a single table
Raster and imagery data types are managed and stored in relational tables as well. Raster
data is typically much larger in size and requires an associated side table for storage. During
the storage process the software cuts the raster into smaller pieces, called "blocks," and
stores them in individual rows in the separate block table.
7. GIS data operations
Following are the different operations used in GIS:
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A GIS consists of a data base coupled with a graphics output. There are three major types
of operations in a GIS:
1.Access methods
The user will want to access data elements with certain properties. There are three
questions involved here. The first is whether the requested data is available in the system.
The second question is how long it will take to find the data. Spatial data structures pose
unusual indexing problems and are a topic unto themselves Usually some variation of a
quadtree (for 2D) or octree (for 3D) is used. The third question is how the user accesses
the data. The conventional query language SQL is sometimes used.
2.Analytical operations
Analytical operations allow the user to combine data to produce new data. The most
important operation is the overlay of different spatial data sets to produce a new data set.
For example, a biologist might want to determine what variables affect the population of
dolphins. For a given part of the ocean, there may be measurements for water temperature,
different fish populations, including predators (sharks), different types of pollution levels,
etc. The biologist could then try to find correlations. Note that this is a multivariate
visualization problem. The analytical operations can also include computations to produce a
new data set.
3. Rendering
Rendering operations show the data as some sort of map with the additional information
displayed. This is where Visualization techniques can be applied to GIS.
4. Interpolation
This interpolation technique is a method where a series of iterations are made over a
surface to smooth it out. There are three options, which can be set for stopping the
iterations whenever any one of the specified conditions is met.
§ The first option specifies the maximum number of iterations the routine should perform
on the map data before stopping.
§ The second option specifies the tolerance for convergence (percent of range) as a
percentage of the range of elevations represented in the map. The routine will stop
when the maximum change in any pixel is less then the specified tolerance. A value of
0.5% for a map with elevations of 3,560 to 5,600 ft. equals a change of 10.2 feet or
less.
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§ The third option is Convergence Tolerance (Absolute) which stops iterations when the
maximum change in any pixel is less than the specified value. The value is given in map
elevation units, usually feet.
5. Class of Proximity analysis
Several classes can be developed to analysis the interest of a particular region like the
determination of signal failure on highway, locating shortest path using shortest path
algorithms using 2D or 3D information are the important classes of proximity analysis.
6. Raster image processing
This process is divided in to two categories:
(1) To produce new map from the existing geographical features on different map layers
algebraically using map algebra.
(2) Digital image analysis is used to detect the edges and objects. For example, detection
of roads in a satellite image of a city.