1. Map Concepts
What is GIS ?
How does a GIS work ?
What’s Special About GIS ?
GIS in action
Introduction to GIS
2. Map Concepts
What is a map?
Map Features
Map Symbology
Map Scale
Map and its elements
3. What is a map ?
Symbolic representation of GIS
4. 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.
6. 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.
8. 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
10. 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.
11. Map and its elements
Title
Legend
Source
North Arrow
Scale
12. 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.
13. “What is GIS ?”
Defining GIS
Describing our world
Who all are involved in GIS
Why GIS needed ?
Data Base
Visualization
Sub-Systems of GIS
14. Defining GIS
A Powerful tool for solving real-world problems
A method to
visualize, manipulate, analyze, and display spatial data
15. 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.
16. 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
17. 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.
19. How the components play …
People
Capture
Store,
Manipulate,
Analyze
Display Data (Spatial and/or Attribute data)
using
Software,
Hardware
procedures.
20. 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
21. 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.
24. 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.
25. Sub-Systems of GIS
Land Information System (LIS)
Environmental Information System (EIS)
Resources Information System
Spatial Data Handling System
AM / FM
Planning Information System
26. How Does GIS Work ?
Sources of GIS data.
Types of GIS data.
Capturing GIS data
Data integration
27. 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
29. Sources of GIS Data
Satellite Image covering part of
the earth
Land Use / Land cover extracted
from the image
30. 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.
31. 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.
32. ◦ 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
36. 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
38. 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
42. 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
43. 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
44. Spatial query: Lung disease in the 1860s
District: Alston with Garrigill
County: Cumberland
M_rate: 68.4
46. 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
49. 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.
51. 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.
52. What’s Special about a GIS
Information retrieval
Networks
3D Analysis
Interpolation
Spatial Analysis
54. Information Retrieval
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.
56. Information Retrieval
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.
57. Information Retrieval
Where is……….(identify based on Conditions) ?
Selection of districts that has total population >
4000000 and Urban Population > 1000000
58. Information Retrieval
Intersect
Are within a distance of
Completely within
Completely contain
Have center in
Are crossed by the outline
of
…. a lot more
63. Solving network problems
Network traces
Trace upstream and downstream
Tracing optimal path
Find problem areas of a network
Building Networks
64. Trace upstream and downstream
Upstream trace Downstream trace
Flag
Results Network
Source/Sink feature
65. Find problem areas of a network
Given the problem areas, finding the root
cause of the problem
Problem Area
66. Building networks
Solve network problems using Geodatabase data
model
Geometric
Network
Lateral
Service
Main
Feed
Valve
Feature
classes
68. 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
69. 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.
