GIS - lecture-1.ppt

 Map Concepts
 What is GIS ?
 How does a GIS work ?
 What’s Special About GIS ?
 GIS in action
Introduction to GIS

Map Concepts
 What is a map?
 Map Features
 Map Symbology
 Map Scale
 Map and its elements

What is a map ?
 Symbolic representation of GIS

What is a map ?
Subjective abstraction of real-world features
Communicates locational and descriptive information
A map is the interface between geographic data and
our perception.
Maps are uniquely capable for sharing knowledge
about our world in many ways
Maps identify what is at a location.
Maps can locate where you are.
Maps let you identify distribution, relationships and
trends not otherwise discernible.
Maps can integrate data from diverse sources into a
common geographic reference.

Map Features
Lines
Roads
Areas
Districts
Points
Towns
Himachal Pradesh

Map Features
 Points : Points define discrete locations of geographic
features which are too small to be depicted as lines or
areas, such as well locations, telephone poles, or
buildings. Points can also represent locations that have no
area, such as mountain peaks.
 Lines : - Lines represent the shape of geographic objects
too narrow to depict as areas, such as streets and streams,
or linear features that have length but no area, such as
elevation contours.
 Areas : - Areas are closed figures that represent the shape
and location of homogenous, real-world features such as
states, cities, parcels, soil types, or land use zones.

Map Symbology
Point symbols Line symbols Polygon shades

 Linear symbols: These are simple lines and modifications of lines.
Some examples include double, dashed, hashed, dotted and solid lines.
 Qualitative area: These are pictorial representations of features with
varying areas.
 Quantitative area: These are shaded areas. The degree (value) of
shading is proportional to the value of represented feature. For
example, sparsely populated areas could be represented by light
shades, and densely populated areas could be represented by dark
shades.
 Dot distributions: These are variations in dot density based on the
value of a map feature. For example, each dot could represent the
number of televisions in a particular area.
 Geometric point: These are geometric shapes such as triangles,
squares, rectangles, circles and stars.
 Pictorial point: These are simplified, scaled down, generic picture of
the feature they represent.
Map Symbology

Map Scale
Large scale (1:50,000) Small scale (1:250,000)

Map Scale
 Scale is defined as the ratio between the distance on the
map to the corresponding distance on the ground.
 The map scale determines the spatial resolution of the
graphic feature represented.
 A small scale map covers larger area showing lesser
details.
 A large scale map covers smaller area showing greater
details.

Map and its elements
 Title
 Legend
 Source
 North Arrow
 Scale

Map and its elements
Title: The title represents the theme of the map
Map: The display of map contents
Legend: Description of map features
Scale: Ratio between map distance to ground
distance
North Arrow: Depicting the true north
Source: Details about the origin of map contents.

“What is GIS ?”
 Defining GIS
 Describing our world
 Who all are involved in GIS
 Why GIS needed ?
 Data Base
 Visualization
 Sub-Systems of GIS

Defining GIS
 A Powerful tool for solving real-world problems
 A method to
visualize, manipulate, analyze, and display spatial data

Definition of GIS
 GIS is a computer system capable of assembling, storing,
manipulating, and displaying geographically referenced
information, i.e. data identified according to their locations.
 Practitioners also regard the total GIS as including
operating personnel and the data that go into the system.
 A GIS stores information about the world as a collection of
themed layers that can be used together.
 A layer can be anything that contains similar features such
as customers, buildings, streets, lakes, etc.
 This data contains either an explicit geographic reference,
such as a latitude and longitude coordinate, or an implicit
reference such as an address, postal code, census tract name,
forest stand identifier, or road name.

Describing our World
Location Information:
Where is it?
51°N, 112°W
We can describe any
element of our world
in two ways:
Attribute Information:
What is it?
Species: Oak
Height: 15m
Age: 75 Yrs

 Location Information: Describes where a particular geographic
feature is situated on Earth, in Spherical coordinate System that is,
Degrees, Minutes, and Seconds.
 This can be converted to Cartesian coordinate system to make a
two-dimensional map.
 Attribute Information: Describes the feature details like what it
is, how much it is, what it contains, etc.
 Geography began in map-making and regional descriptions, but
has been transformed by the advancement of science, the
development of computers, and global environmental change.
 Today, geographers combine natural science, social studies, and
information technologies to understand our changing world.

Components
Spatial Data
Procedures
Attribute
Data
People
Software &
Hardware

How the components play …
People
 Capture
 Store,
 Manipulate,
 Analyze
 Display Data (Spatial and/or Attribute data)
using
 Software,
 Hardware
 procedures.

Why GIS is Needed ….
Maps are :
 still difficult to update
 storage is a problem
 likely to fade, torn and shrink
 human to interpret the relationship between features with
 static data shown on the map …
… where as GIS :
 makes maps dynamic
 displays map information
 interactively
 build the spatial relationship between features
 analyze to answer real-world problems

Why is GIS Needed ….
 On paper maps, each color, pattern, picture, or label
gives you information about the features.
 But, the amount of information we can get from a paper
map is limited to what is shown and so maps are static.
 GIS map display on a computer screen looks like any
other map.
 However, with a GIS map display, we can get detailed
information about each feature.
 With GIS you can find features based on their
attributes and analyze feature locations to uncover
relationships between them.

Database
“Not Easy to Interpret”

Visualization –
“Worth a Thousand Words”
“Smart Maps”

Visualization
 After linking the attribute information to the themed layers
the static maps becomes dynamic and they respond to user
queries – Smart Maps.
 The link between features and attributes is dynamic.
 The link between features and attributes is a two-way
relationship, changing an attribute in the table automatically
results in a change on the map.

Sub-Systems of GIS
 Land Information System (LIS)
 Environmental Information System (EIS)
 Resources Information System
 Spatial Data Handling System
 AM / FM
 Planning Information System

How Does GIS Work ?
 Sources of GIS data.
 Types of GIS data.
 Capturing GIS data
 Data integration

Sources of GIS Data
 Digitized and Scanned Maps
i. purchased, donated, Internet
ii. created by user
 Data Bases – Tables of data
 GPS – Global Positioning System
i. accurate locations
 Field Sampling of Attributes
 Remote Sensing & Aerial Photography

Sources of GIS Data
 Toposheet  Traced Road Map

Sources of GIS Data
 Satellite Image covering part of
the earth
 Land Use / Land cover extracted
from the image

Sources of GIS Data
 A GIS, which can use information from many different sources, in many
different forms can help with GIS analyses.
 The primary requirement for the source data is that the locations for the
variables are known.
 Location may be annotated by x,y, and z coordinates of longitude,
latitude, and elevation, or by highway mile markers.
 Any variable that can be located spatially can be fed into a GIS.
 Several computer data bases that can be directly entered into a GIS are
being produced by many firms.
 Different kinds of data in map form can be entered into a GIS.
 A GIS can also convert existing digital information, which may not yet
be in map form, into forms it can recognize and use.
 For example, digital satellite images can be analyzed to produce a map
like layer of digital information about vegetative covers.

 Raster – Grid
 “pixels”
 a location and value
 Satellite images and aerial photos are
already in this format
Types of GIS Data
Two Main Types
Real world
 Vector – Linear
 Points, lines & polygons
 “Features” (house, lake, etc.)
 Attributes
• size, type, length, etc.

◦ Two types of data are stored for each item in the
database
 1. Attribute data:
◦ Says what a feature is
 Eg. statistics, text, images, sound, etc.
 2. Spatial data:
◦ Says where the feature is
◦ Co-ordinate based
◦ Vector data – discrete features:
Points
Lines
Polygons (zones or areas)
◦ Raster data:
 A continuous surface

Geo-referencing data
 Capturing data
Scanning: all of map converted into raster data
Digitising: individual features selected from map
as points, lines or polygons
 Geo-referencing
Initial scanning digitising gives co-ordinates in
inches from bottom left corner of digitiser/scanner
Real-world co-ordinates are found for four
registration points on the captured data
These are used to convert the entire map onto a
real-world co-ordinate system

Example of geo-referencing
Source: ESRI (1997)

Layers
 Data on different themes are stored in
separate “layers”
 As each layer is geo-referenced layers from
different sources can easily be integrated
using location
 This can be used to build up complex
models of the real world from widely
disparate sources

Raster data: Hastings
Scale: 1:100,000
Grid cell size: 50 m.
Minimum altitude: 0 m.
Maximum altitude: 174 m.

Layers and book history
Source: MacDonald & Black 2000:

Querying GIS data
 Attribute query
Select features using attribute data (e.g. using SQL)
Results can be mapped or presented in conventional
database form
Can be used to produce maps of subsets of the data or
choropleth maps
 Spatial query
Clicking on features on the map to find out their
attribute values
 Used in combination these are a powerful way of
exploring spatial patterns in your data

Attribute query: Lung disease in the 1860s
 Spatial data:
Registration Districts,
1/1/1870
 Attribute data:
Mortality rate per 1,000
from lung disease among
men aged 45-64
 Source: Registrar
General’s Decennial
Supplement, 1871
 Query: Select areas
where mortality rate >
58.0

Spatial query: Lung disease in the 1860s
District: Alston with Garrigill
County: Cumberland
M_rate: 68.4

Mapping through attribute query

Data integration: Overlay
 Joins two layers to create a new layer
 The output layer will contain both the spatial AND
attribute data from both of the input layers

Capturing GIS Data
 Digitization
 Scanning

 How can a GIS use the information in a map?
 If the data to be used are not already in digital
form
The computer can recognize, various
techniques can capture the information.
Maps can be digitized on screen or on digitizer
board, to collect the coordinates of features.
Electronic scanning devices will also convert
map lines and points to digits.

 The data procured from different sources and
captured into an GIS environment
 however, not be readily usable, till it is
integrated into one single system.
 A GIS makes it possible to link, or integrate,
information that is difficult to associate through
any other means.
 GIS can use combinations of mapped variables
to build and analyze new variables.

What’s Special about a GIS
 Information retrieval
 Networks
 3D Analysis
 Interpolation
 Spatial Analysis

Information Retrieval
 What is it ….?

 Once the spatial (Map) and attribute data are
linked,
 To using GIS one can retrieve information about
a feature just by clicking on it.
 This is known as identifying a feature.
 Map features can also be linked to other
information like pictures, documents, video files,
URLs pertaining to that area.
 This information can be retrieved in a presentable
format.

 Where is…(find)?
Patiala

 Suppose you want to locate ANY PLACE in a world
map GIS can help you in searching for it.
 GIS searches the corresponding database of the
theme,
 when a match is found the corresponding feature is
highlighted.

 Where is……….(identify based on Conditions) ?
Selection of districts that has total population >
4000000 and Urban Population > 1000000

 Intersect
 Are within a distance of
 Completely within
 Completely contain
 Have center in
 Are crossed by the outline
of
 …. a lot more

Multiple databases can be Linked and Related

Networks
 Optimal Routing
 Finding Closest Facilities
 Finding Service Areas
 Tracing the networks

Solving network problems
 Network traces
 Trace upstream and downstream
 Tracing optimal path
 Find problem areas of a network
 Building Networks

Trace upstream and downstream
Upstream trace Downstream trace
Flag
Results Network
Source/Sink feature

Find problem areas of a network
 Given the problem areas, finding the root
cause of the problem
Problem Area

Building networks
 Solve network problems using Geodatabase data
model
Geometric
Network
Lateral
Service
Main
Feed
Valve
Feature
classes

3D Mine with Well Data
3D Analysis

 Using the elevation information for points, lines
and polygon feature
GIS can generate 3D models which can be used in
deriving slope, aspect and visibility analysis.
3D Analysis

Interpolation
 It is difficult to relate wetlands maps to rainfall amounts
recorded at different points such as airports, television
stations, and high schools.
 A GIS, however, can be used to depict two- and three-
dimensional characteristics of the Earth's surface, subsurface,
and atmosphere from information points.
 For example, a GIS can quickly generate a map with lines
that indicate rainfall amounts.
 Such a map can be thought of as a rainfall contour map.
 Many sophisticated methods can estimate the characteristics
of surfaces from a limited number of point measurements.
 A two-dimensional contour map created from the surface
modeling of rainfall point measurements may be overlain and
analyzed with any other map in a GIS covering the same
area.

Interpolation
Interpolated Rain Fall Map
Rain Guage Data

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