GIS and Mapping Software Introduction

GIS and Mapping Software
Introduction

Objective

 To provide background on GIS and introduce
QGIS

Geographic Information System (GIS) is an integration
of five basic components

GIS is more than just a computer program that produces maps.

Capturing Analyzing

Storing Displaying

Querying Outputting

A GIS combines layers of spatial data

Answers questions by comparing layers

Querying Data
Identify features based on location

Identify features based on a condition
An African country with a population greater than 300,000

Graphs
Displaying Data
Maps

Tables

Analyzing Data

Proximity

Overlay

Network

Representing the Natural World in GIS Data

GIS data types – Vector Data
• Points • Polygons
• water supply wells • Lakes
• Village centers • Village areas

• Lines
• Water lines
• Road center

GIS data types – Raster Data
• An array of cells
• Represents continuous data layer
• Best for data without easily defined boundaries
• Each cell has one value

Comparison of 2 ways of representing GIS data

Vector

Raster

Vector Data

 Vector data provides a complex representation of
the world it stores both:
 Attributes -- text or numerical information that
describe the features (population of a village or
number of orphans in a province)
 Geometry -- the shape or position of the features
(boundary of a country or location of a hospital)

Attributes
 Nonspatial information about a geographic
feature in a GIS
 Stored in a table and linked to the feature by a
unique identifier
 For example, attributes of a river might include its
name, length, and basin.
Unique_ID River name Length_km Basin_km2
1 Mississippi 3,730 2,981,076
2 Amazon 6,937 7,050,000
3 Niger 4,180 2,117,700

17

Linking geometry and attributes
• Unique identifier links geometry and attributes

FID = 60
(Feature Identifier)

Shapefile data format (vector data)
 Actually, multiple files
 Attributes stored in dBASE table (.dbf file format)
Shapefile.dbf table

Hospital
shapefile
“Shape” field
Access separate
Coordinate file

Topology

 The arrangement that constrains how point, line, and
polygon features in a vector data file share geometry.

 Topology defines and enforces data integrity rules
(for example, there should be no gaps between
polygons).

Raster Data: Images and grids
 Rows and columns of equally-sized cells
 Each cell stores a value
 Detail depends on cell size

Can be stored in various image file formats
including: JPG, IMG, TIF, ASC, BMP, etc

Village-wise Slide Positivity Rate (M alaria) of Trans-Yamuna Region
Rasters 2002 2004
Images Data based grids

Low High

Open Source GIS Software

 Diva GIS
 Dev-Info
 Health Mapper
 E2G
 QGIS
 others?

Open source GIS software
Software Notes
QGIS Easy to learn; training materials available; active
user community writing modules

DIVA GIS Best suited for point data; limited data
classification methods; robust point analysis
capabilities
Dev-Info Mainly a data display tool, limited GIS
capabilities
Health Mapper WHO mapping program; no planned updates;
transitioning to DHIS- II
EPI Map Module in Epi-Info; limited GIS capabilities, best
suited for Epi-Info users

Key Points
 GIS is an integration of 5 components
 GIS represents the world as layers
 Data can be stored as raster or vector
 There are standard features that should be
present in a GIS:
 Storing, Querying, Displaying, Outputting Data

Any questions?

GIS and Mapping Software Introduction

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