Introduction to Geographic Information Systems

I. Introduction: Fundamentals of GIS
1. Definition: GIS
 GIS (Geographic Information System): is computer
assisted system used for collecting, storing, retrieving
at will, transforming and displaying spatial data from
the real world for a particular set of purpose.
It is an organized collection of computer hardware,
software, geographical data, personal designed to
efficiently capture, store, update, manipulate,
analyze and display all form of geographically
referenced information

GEOGRAPHIC:
implies that locations of the data items are known, or can be calculated, in terms of Geographic
coordinates (Latitude, Longitude)
SYSTEM:
implies that a GIS is made up from several inter-related and linked components with different
functions. Thus, GIS have functional capabilities for data capture, input, manipulation,
transformation, visualization, combinations, query, analysis, modelling and output.
INFORMATION :
implies that the data in a GIS are organized to yield useful knowledge, often as colored maps and
images, but also as statistical graphics, tables, and various on-screen responses to interactive
queries.
1. Definition: GIS

GIS = Geographic Information System
Links databases and maps
Manages information about places
Helps answer questions such as:
 Where is it?
 What else is nearby?
 Where is the highest concentration of ‘X’?
 Where can I find things with characteristic ‘Y’?
 Where is the closest ‘Z’ to my location?
1. Definition: GIS
The objective: to improve overall decision making

It is software designed to assist in the process of designing and drawing maps or the generation,
storage and editing of maps using a computer.
 Cheap
 Quick
 Making maps specific to the user
 Making map possible in the absence of
skilled persons
 Allows experimentation with different
graphical representation of the same area
 Map making and updating easier if the data
are in digital form.
 Facilitate analyses of data that demand
interaction between statistical analyses and
mapping
 Storage of data in digital form
 Creates 3D maps
Advantages
1. Definition: Computer assisted mapping

Contributing Disciplines & Technologies
GIS is a multi-disciplinary concept built on convergence of technological and
traditional disciplines. GIS has been called an ‘enabling technology’ because of the
potential it offers for wide variety of disciplines which must deal with integration,
modeling and analysis of spatial data.
• Geography,
• Cartography,
• Remote sensing,
• Photogrammetry,
• Surveying,
• Geodesy,
Contributing
disciplines
• Statistics,
• Operations research,
• Computer science,
• Mathematics,
• Civil engineering.

2. Historical background:
The first application of the concept was in 1832 when Charles
Picquet created a map representing cholera outbreak across 48
districts of Paris. This map was an early version of a heat map,
which would later revolutionize several industries.
The Beginnings of Spatial Analysis
Inspired by Picquet, John Snow adopted the same principle to depict
cholera deaths in London in 1854. He evolved the concept by
presenting an argument developed from a spatial analysis of data.

2. Historical background: When was the term GIS first used?
In the early 20th century, a printing technique called photozincography was introduced, which
allowed users to separate layers from a map. This technology meant different themes could be
printed, but it did not represent a full GIS since there was no opportunity to analyze mapped
data.
The concept of GIS was first introduced in the early 1960s, and it was subsequently researched
and developed as a new discipline. The GIS history views Roger Tomlinson as a pioneer of the
concept, where the first iteration was designed to store, collate (arrange), and analyze data
about land usage in Canada.
The second phase of development in GIS history occurred throughout the 1970s, and by the
1980s the concept progressed as national agencies adopted it, and invested parties began
determining best practice. By the late 1980s, there was a focus on improving the usability of
technology and making facilitates more user-centric.

2. Historical background: When was the term GIS first used?
There is little widespread information available on how the technology has been adopted and
deployed.
As the system continuously advanced in Canada throughout the 1970s and 1980s, by the 1990s it
was driven by mainframe hardware, with data sets from the entire Canadian landmass.
Those pursuing development in the field of GIS had different goals, meaning there was no set
direction for research to follow. A single path finally surfaced when GIS became the focus of
commercial activity with satellite imaging technology. Mass applications were thus initiated for
business and private use.

2. Historical background: Desktop GIS & Widespread Adoption
Throughout the 1990s, software company Esri released ArcView, a desktop solution for mapping
systems. The influx of the Internet saw widespread adoption of GIS heading into the millennium,
and the technology reached governmental authorities.
Many companies, such as Nobel Systems, adopted
the technology to provide services to cities,
municipalities and private organizations to
manage assets in the field, gather business
intelligence, and easily send data to the company
headquarters to analyze.

3. Components of GIS
In general, GIS constitutes four major components including:
computer hardware, set of application software , data and
people.
The hardware for a GIS includes:
• Computer,
• Input devices like digitizer (for vectorisation of
given map) and scanner (to convert maps into
*.tiff, *.bmp, and *.jpg for onscreen digitization)
and
• Output devices such as plotter, DeskJet printer,
colour laser printer etc.
a) Hardware

Chap. I. Introduction: Fundamentals of GIS
3. Components of GIS
b) Software
The GIS software package has a set of modules for performing digitization, editing, overlaying
and conversion, analysis and for answering the queries, and generating output.
Software may be chosen on the objective and also the cost of the software. GIS software is
available as freeware (GRASS), low cost MapInfo for small scale GIS works and expensive
ArcInfo for extension GIS analysis.
Common GIS software packages,
 ArcGIS:
 most popular and widely used GIS software
 Very expensive
 Friendly graphical user interface (GUI)
 MapInfo:
 Vector based , desktop GIS ,emerging web
mapping capabilities
 IDRISI: good Raster capabilities ,weak vector
capabilities and the interface not quite as user friendly
as ArcGIS
 GRASS: Primarily Raster based , open source ,
free.
 QGIS

4. GIS Process & Capabilities
Data Capture
Convert Data to
Digital Format
Store Data in
Computer
Register Map
Base
Process
Data
Interpret
Data
Display
Results
GIS Process

5. GIS Process & Capabilities
A well designed GIS should be able to provide(capability)
 Quick and easy access to large volume of data
 The ability to select detail by area or theme
 The ability to link or merge one data set with another
 The ability to analyze spatial characteristics of data
 The ability to search for particular characteristics or feature in an area
 The ability to update data quickly and cheaply
 The ability to model data and access alternatives
Output capabilities(maps, graphs, address lists and summary statistics)
tailored to meet particular needs

1. Maps and Spatial data
A Map is the graphic representation of earth’s surface or
any planet (space body)’s surface, as a whole, or part of it
on a plane surface drawn to a scale and projection with
suitable sign and symbols, so that each and every point
represented on it corresponds to its terrestrial or celestial
position.
Spatial data, also known as geospatial data, is a term used to describe any data related to or
containing information about a specific location on the Earth’s surface.
It is an information about a physical object that can be represented by numerical values in a
geographic coordinate system.
Chap. II. Spatial Data Structure

Generally speaking, spatial data represents the location, size and shape of an object on planet
Earth such as a building, lake, mountain or township. Spatial data may also include attributes that
provide more information about the entity that is being represented. Geographic Information
Systems (GIS) or other specialized software applications can be used to access, visualize,
manipulate and analyze geospatial data.
Spatial data can exist in a variety of formats and contains more than just location specific
information. To properly understand and learn more about spatial data, there are a few key
terms that will help you become more fluent in the language of spatial data.
1. Maps and Spatial data

1. Spatial data Models
i) Vector
Vector data is best described as graphical
representations of the real world.
There are three main types of vector data:
• Points,
• Lines,
• Polygons.
Vectors are best used to present generalizations of objects or features on the Earth’s surface.
Vector data and the file format known as shapefiles (.shp) are sometimes used interchangeably
since vector data is most often stored in .shp files.
Connecting points create lines, and connecting lines that create an enclosed area create
polygons.

1. Data & Metadata
Data is an important component of any GIS. GIS is capable accepting any form of data i.e. digital
data supplied by satellites, vectorisation of existing maps, data from Global Positioning System
(GPS), as well as statistical data published by government departments. The quality of the
information furnished by a GIS is directly related to quality of the data used.
Geospatial data tells you where it is and attribute data tells you what it is. Metadata describes
both and attributes data.

2. Spatial data Models
ii) Raster
Raster data is data that is presented in a grid of pixels.
Each pixel within a raster has a value (DN: Digital
Number), whether it be a colour or unit of
measurement, to communicate information about the
element in question.
Rasters typically refer to imagery. However, in the
spatial world, this may specifically refer to orthoimagery
which are photos taken from satellites or other aerial
devices. Raster data quality varies depending on
resolution and your task at hand.

3. Non Spatial data: Attribute
Spatial data contains more information
than just a location on the surface of the
Earth. Any additional information, or
non-spatial data, that describes a feature
is referred to as an attribute. Spatial data
can have any amount of additional
attributes accompanying information
about the location.
For example, you might have a map displaying buildings within a city’s downtown region. Each of
the buildings, in addition to their location, may have additional attributes such as the type of use
(housing, business, government, etc.), the year it was built, and how many stories it has.
Chap. II. GIS Data Structure

Chap. III. Coordinate Systems
Locations on the Earth's surface are measured and represented in terms of coordinates. A
coordinate is a set of two or more numbers that specifies the position of a point, line, or other
geometric figure in relation to some reference system.
Coordinate systems enable geographic datasets to use common locations for integration. A
coordinate system is a reference system used to represent the locations of geographic features,
imagery, and observations, such as Global Positioning System (GPS) locations, within a common
geographic framework.
Each coordinate system is defined by the following:
 Its measurement framework, which is either geographic or geocentric (in which spherical
coordinates are measured from the earth's center) or planimetric or projected (in which the
earth's coordinates are projected onto a two-dimensional planar surface)
1. Introduction

 Units of measurement (typically feet or meters for projected coordinate systems or decimal
degrees for latitude-longitude)
 The definition of the map projection for projected coordinate systems
 Other measurement system properties such as a ellipsoid of reference, a datum, one or more
standard parallels, a central meridian, and possible shifts in the x- and y-directions
Several hundred geographic coordinate systems and a few thousand projected coordinate
systems are available for use. In addition, you can define a custom coordinate system.
1. Introduction

2. Types of Coordinate system
The following are two common types of coordinate systems used in a Geographic Information System (GIS):
 A global or spherical coordinate system such as latitude-longitude. These are often referred to as geographic
coordinate systems.
 A projected coordinate system such as universal transverse Mercator (UTM), ITRF 2005 (International Terrestrial
Reference Frame), all of which (along with numerous other map projection models) provide various mechanisms
to project maps of the earth's spherical surface onto a two-dimensional Cartesian coordinate plane. Projected
coordinate systems are referred to as map projections.
Coordinate systems (both geographic and projected) provide a framework for defining real-world
locations.
What is a spatial reference?
A spatial reference is a series of parameters that define the coordinate system and other spatial properties for each
dataset in the geodatabase. It is typical that all datasets for the same area (and in the same geodatabase) use a
common spatial reference definition.

A spatial reference includes the following:
 The coordinate system
 The coordinate precision with which coordinates are stored (often referred to as the coordinate resolution)
 Processing tolerances (such as the cluster tolerance)
 The spatial extent covered by the dataset (often referred to as the spatial domain)
i) Geographic coordinate systems (GCS)
2. Types of Coordinate system
A geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth. A
GCS includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid). The spheroid
defines the size and shape of the earth model, while the datum connects the spheroid to the earth's surface.
A point is referenced by its longitude and latitude values. Longitude and latitude are angles measured from the
earth's center to a point on the earth's surface. The angles often are measured in degrees (or in grads). The
following illustration shows the world as a globe with longitude and latitude values:

In the spherical system, horizontal lines, or east–west lines, are lines of equal latitude, or parallels. Vertical lines, or
north–south lines, are lines of equal longitude, or meridians. These lines encompass the globe and form a gridded
network called a graticule.
The line of latitude midway between the poles is called the equator. It defines the line of zero latitude. The line of
zero longitude is called the prime meridian. For most GCSs, the prime meridian is the longitude that passes through
Greenwich, England. The origin of the graticule (0,0) is defined by where the equator and prime meridian intersect.
Latitude and longitude
The "latitude" (Lat., φ, or phi) of a point on Earth's surface is the angle between
the equatorial plane and the straight line that passes through that point and
through (or close to) the center of the Earth. Lines joining points of the same
latitude trace circles on the surface of Earth called parallels, as they are parallel
to the Equator and to each other. The North Pole is 90° N; the South Pole is
90° S. The 0° parallel of latitude is designated the Equator, the fundamental
plane of all geographic coordinate systems. The Equator divides the globe
into Northern and Southern Hemispheres.

The "longitude" (abbreviation: Long., λ, or lambda) of a point on Earth's surface is the angle east or west of a
reference meridian to another meridian that passes through that point. All meridians are halves of
great ellipses (often called great circles), which converge at the North and South Poles. The meridian of
the British Royal Observatory in Greenwich, in south-east London, England, is the international prime meridian,
although some organizations—such as the French Institut Géographique National—continue to use other meridians
for internal purposes.
The prime meridian determines the proper Eastern and Western Hemispheres, although maps often divide these
hemispheres further west in order to keep the Old World on a single side.
The antipodal meridian of Greenwich is both 180°W and 180°E. This is not to be
conflated with the International Date Line, which diverges from it in several places
for political and convenience reasons, including between far eastern Russia and the
far western Aleutian Islands.
The combination of these two components specifies the position of any location on
the surface of Earth, without consideration of altitude or depth. The grid formed
by lines of latitude and longitude is known as a "graticule".[The origin/zero point
of this system is located in the Gulf of Guinea about 625 km (390 mi) south
of Tema, Ghana.

Length of a degree
On the GRS80 or WGS84 spheroid at sea level at the Equator, one latitudinal second measures 30.715 meters, one
latitudinal minute is 1843 meters and one latitudinal degree is 110.6 kilometers. The circles of longitude,
meridians, meet at the geographical poles, with the west-east width of a second naturally decreasing as latitude
increases. On the Equator at sea level, one longitudinal second measures 30.92 meters, a longitudinal minute is
1855 meters and a longitudinal degree is 111.3 kilometers. At 30° a longitudinal second is 26.76 meters, at
Greenwich (51°28′38″N) 19.22 meters, and at 60° it is 15.42 meters.
Geographic (datum) transformations
If two datasets are not referenced to the same geographic coordinate system, you may need to perform a
geographic (datum) transformation. This is a well-defined mathematical method to convert coordinates between
two geographic coordinate systems. As with the coordinate systems, there are several hundred predefined
geographic transformations that you can access. It is very important to correctly use a geographic transformation if
it is required. When neglected, coordinates can be in the wrong location by up to a few hundred meters. Sometimes
no transformation exists, or you have to use a third GCS like the World Geodetic System 1984 (WGS84) and combine
two transformations.

ii) Projected coordinate systems (PCS)
A projected coordinate system (PCS) is defined on a flat, two-dimensional surface. Unlike a GCS, a PCS has constant
lengths, angles, and areas across the two dimensions. A PCS is always based on a GCS that is based on an
ellipsoid. In addition to the GCS, a PCS includes a map projection, a set of projection parameters that customize the
map projection for a particular location, and a linear unit of measure.
UTM (Universal Transversal Mercator) and ITRF 2005 are examples of PCS. In Rwanda, we use UTM-35S, UTM-36S
and ITRF 2005 (TM-Rwanda)

3. Map projections & Transformation
Whether you treat the earth as a sphere or a ellipoid, you must transform its three-dimensional surface to create a
flat map sheet. This mathematical transformation is commonly referred to as a map projection. One easy way to
understand how map projections alter spatial properties is to visualize shining a light through the earth onto a
surface, called the projection surface. Imagine the earth's surface is clear with the graticule drawn on it. Wrap a
piece of paper around the earth. A light at the center of the earth will cast the shadows of the graticule onto the
piece of paper. You can now unwrap the paper and lay it flat. The shape of the graticule on the flat paper is different
from that on the earth. The map projection has distorted the graticule.
An ellipsoid cannot be flattened to a plane any more easily than a piece of orange peel can be flattened—it will tear.
Representing the earth's surface in two dimensions causes distortion in the shape, area, distance, or direction of the
data. A map projection uses mathematical formulas to relate spherical coordinates on the globe to flat, planar
coordinates. Different projections cause different types of distortions. Some projections are designed to minimize
the distortion of one or two of the data's characteristics. A projection could maintain the area of a feature but alter
its shape.

a) Metric properties of map
Many properties can be measured on the Earth's surface independent of its geography:
 Area
 Shape
 Direction
 Bearing
 Distance
Map projections can be constructed to preserve some of these properties at the expense of others. Because the
curved Earth's surface is not isometric to a plane, preservation of shapes inevitably leads to a variable scale and,
consequently, non-proportional presentation of areas. Vice versa, an area-preserving projection can not
be conformal (keeping angles unchanged), resulting in shapes and bearings distorted in most places of the map.
Each projection preserves, compromises, or approximates basic metric properties in different ways. The purpose of
the map determines which projection should form the base for the map. Because many purposes exist for maps, a
diversity of projections have been created to suit those purposes.

Another consideration in the configuration of a projection is
its compatibility with data sets to be used on the map. Data
sets are geographic information; their collection depends on
the chosen datum (model) of the Earth. Different datums
assign slightly different coordinates to the same location, so
in large scale maps, such as those from national mapping
systems, it is important to match the datum to the projection.
The slight differences in coordinate assignation between
different datums is not a concern for world maps or other vast
territories, where such differences get shrunk to
imperceptibility.

b) Design and construction
The creation of a map projection involves two steps:
 Selection of a model for the shape of the Earth or planetary body (usually choosing between
a sphere or ellipsoid). Because the Earth's actual shape is irregular, information is lost in this step.
 Transformation of geographic coordinates (longitude and latitude) to Cartesian (x,y) or polar plane coordinates.
In large-scale maps, Cartesian coordinates normally have a simple relation to eastings and northings defined as a
grid superimposed on the projection. In small-scale maps, eastings and northings are not meaningful, and grids are
not superimposed.
C) Choosing a projection surface
A surface that can be unfolded or unrolled into a plane or sheet without stretching, tearing or shrinking is called
a developable surface. The cylinder, cone and the plane are all developable surfaces.
The sphere and ellipsoid do not have developable surfaces, so any projection of them onto a plane will have to
distort the image. (To compare, one cannot flatten an orange peel without tearing and warping it.)
One way of describing a projection is first to project from the Earth's surface to a developable surface such as a
cylinder or cone, and then to unroll the surface into a plane.

While the first step inevitably distorts some properties of the globe, the developable surface can then be unfolded
without further distortion.
i) Cylinder projection

UTM: Universal Transversal Mercator

ii) Conical Projection

iii) Polar Projection

Introduction to Geographic Information Systems

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