GIS for NRM

N.D.K. Dayawansa

GIS--What is it?

• Geographic/Geospatial Information

– information about places on the earth’s surface

– knowledge about “what is where when”

– Geographic/geospatial: synonymous

• GIS--what’s in the S?

– Systems: the technology

– Science: the concepts and theory

– Studies: the societal context

The World Geographic Knowledge

Citizens

Inventory

Decision Support

Geographic Information Technologies • Global Positioning Systems (GPS)

– a system of earth-orbiting satellites which can provide precise (100 meter to sub-cm.) location on the earth’s surface (in lat/long coordinates or equiv.)

• Remote Sensing (RS) – use of satellites or aircraft to capture information about the

earth’s surface

– Digital ortho images a key product (map accurate digital photos)

• Geographic Information Systems (GIS) – Software systems with capability for input, storage,

manipulation/analysis and output/display of geographic (spatial) information

GPS and RS are sources of input data for a GIS.

Geographic Information Systems (GIS) Definitions

• The common ground between information processing and the many fields using spatial analysis techniques. (Tomlinson, 1972)

• A powerful set of tools for collecting, storing, retrieving, transforming, and displaying spatial data from the real world (Burroughs, 1986)

• A computerised database management system for the capture, storage, retrieval, analysis and display of spatial (locationally defined) data. (NCGIA, 1987)

• A decision support system involving the integration of spatially referenced data in a problem solving environment. (Cowen, 1988)

Decision

GIS Process Output

GIS analysis

Import or build datasets

Define GIS criteria

Define problem

Decision

GIS Process Output

GIS analysis

Import or build datasets

Define GIS criteria

Define problem

Geographic Information Systems

Why Study GIS? • Many government activities estimated to be geographically based

– zoning, public works (streets, water supply, sewers), garbage collection, land ownership and valuation, public safety (fire and police)

– natural resource management – highways and transportation

• businesses use GIS for a very wide array of applications – retail site selection & customer analysis – logistics: vehicle tracking & routing – natural resource exploration (petroleum, etc.) – precision agriculture

– civil engineering and construction

• Military and defense – Battlefield management – Satellite imagery interpretation

• scientific research employs GIS – geography, geology, botany – anthropology, sociology, economics, political science – Epidemiology, criminology

Examples of Applied GIS

• Urban Planning, Management & Policy – Zoning, subdivision planning – Land acquisition – Economic development – Code enforcement – Housing renovation programs – Emergency response – Crime analysis – Tax assessment

• Environmental Sciences – Monitoring environmental risk – Modeling stormwater runoff – Management of watersheds,

floodplains, wetlands, forests, aquifers – Environmental Impact Analysis – Hazardous or toxic facility siting – Groundwater modeling and

contamination tracking • Political Science

– Redistricting – Analysis of election results – Predictive modeling

• Civil Engineering/Utility – Locating underground facilities – Designing alignment for freeways, transit – Coordination of infrastructure maintenance

• Business – Demographic Analysis – Market Penetration/ Share Analysis – Site Selection

• Education Administration – Attendance Area Maintenance – Enrollment Projections – School Bus Routing

• Real Estate – Neighborhood land prices – Traffic Impact Analysis – Determination of Highest and Best Use

• Health Care – Epidemiology – Needs Analysis – Service Inventory

History of GIS Dr. John Snow

and the 1854 Cholera outbreak in London's Broad Street region

Dr John Snow is known as the ‘father of modern epidemiology’ and the ‘father of GIS’

He mapped the 1854 Cholera outbreak in London’s Broad Street region.

An outbreak of choledra in London in 1854 in the Soho district was typical of the time, and the deaths it caused are shown in the map.

Source: John Snow Inc. www.jsi.com

Source: UCLA http://www.ph.ucla.edu/epi/snow/snowmap1_1854_lge.htm

Text source: Longley et al (2005)

Dr John Snow

Dr. Snow noticed that the outbreak appeared to be centred on a public drinking water pump in Broad Street –

The pattern shown on the map would reflect the locations of people who drank the pump’s water.

Deaths had occurred in households that were located closer to other sources of water, but but their source of water is also the Broad Street pump.

Text source: Longley et al (2005

Source: http://www.gisdevelopment.net/application/health/overview/images/image1.jpg

Source: http://blogs.esri.com/Info/photos/geography_matters/images/1440/secondarythumb.aspx

History of computers + GIS

Early maps – evidence of use of spatial data Post 1960s = computerized systems of cataloging and analyzing datasets, including geographic data , begin to be developed and used

History of computers + GIS Early 1970’s: Landsat satellite was launched which was

capable of providing data on the earth surface

Late 1970’s/early 1980’s: development of integrated software

or computer code in publicly or commercially available

packages

ex. ERDAS (1978) by Leica-Geosystems

ex. ArcInfo by ESRI (1981/82)

ex. GRASS by US Army Corp (1982/1985)

ex. MAPINFO (1986)

ex. IDRISI (1987) by Clark Univserity, MA

Source:

bertalya.staff.gunadarma.ac.id

What is GIS? Some definitions of GIS focus on the hardware, software, data and analysis of components. However, no GIS exist in isolation from the organizational context, and there must always be people to plan, implement and operate the system as well as make decision based on the output.

A Geographic Information System is not only about computers, software and electronic data.

A GIS is an organised collection of :

– Hardware

– Software

– Network

– Data

– Procedures

– people!

Source: Longley et al (2005) Geographic Information Systems and Science. 2nd Edition. John Wiley and Sons Ltd.

Capabilities of GIS

• GIS will help to ask spatial questions that may be answered with one, two or more spatial data layers.

Example 1: Where is a given feature or set of features? "Where are forest stands greater than 100 years of age?" In the following dialog, I have specified a query asking for stands whose age in 1998 ("Age_1998") is greater than 100 years.

The records that have matched the query criteria are displayed on the map in the default selection color of yellow.

Example 2: What features are at a given location? "What is the age of the forest near the 1050 Road?" The process is similar to the selection of stands within a certain age range, except first a particular road (the 1050 Road) is selected.

Once the road is selected, we can use the spatial location of the selected road to make yet another selection against forest stands. The spatial selection will be all stands within 5 m of the selected road segment.

The following graphic shows a series of selected stands near the 1050 Road. The stands show up on the map in the selection color of yellow. To the lower left, the attribute table for

the stands layer shows records for the selected stands. The age in 1998 is displayed in one of the fields. At the upper left is a selection of all the attributes of one particular stand.

Example 3: Where are areas that meet a given complex set of criteria? "What parts of the forest are located on > 30% slope, closer than 100 ft to a stream, and farther than 50 ft from a road?" The following graphic displays 10% slope classes. These were generated by a simple process performed on a digital elevation model.

These three datasets are merged; all properties of each dataset are stored in the final output. Each yellow polygon is coded for its status in each buffer type, as well as its slope class. Here is a display of a selection of polygons meeting our specified criteria:

Example 5: How can watershed analysis data be generated within a GIS? "What are the road and stream densities (mi / sq. mi) for the forest area? First, we eliminate roads and streams that are not within the forest area. This image shows streams and roads clipped to the administrative boundary of Pack Forest.

Then we summarize the forest area (in square miles) and summarize the stream and road length (in miles). The quotient of (stream length / forest area) is the stream density, and (road length / forest area) is the road density:

area

length

density

forest 6.67 mi ^2

roads 54 mi

8.13 mi / mi^2

streams 31 mi

4.62 mi / mi^2

Spatial data models

two fundamental approaches:

raster model

vector model

Spatial Data Models

• Field-based models (e.g. RASTER) – Continuous spatial phenomena

– For every point in space a value of the field can be determined

– Composite model

• Object-based models (e.g. VECTOR) – Space is populated by well distinguishable,

discrete, bounded objects, geo-relational model

Raster view of the world...

A raster dataset with cells half as large (e.g., 10 m on a side instead of 20 m on a side) may take up 4 times as much storage space, because it takes four 10 m cells to fit in the space of a single 20 m cell. The following image shows the difference in cell sizes, area, and number of cells for two configurations of the same total area:

Raster view of the world...

Tessellation

Raster Features

Sampling

raster model

The entity information is

explicitly recorded for a

basic data unit

(cell, grid or pixel)

• digital orthophoto

• digital elevation model (DEM)_

A few different types of raster data

Vector model

• In a vector-based GIS data are handled as:

– Points X,Y coordinate pair + label

– Lines series of points

– Areas line(s) forming their boundary (series of polygons)

line

feature

area

feature point feature

vector model

Points: represent discrete point features

airports are point features each point is stored as a

coordinate pair

each point location has a record in the table

Lines: represent linear features

roads are linear features

each road segment has a record in the table

Polygons: represent bounded areas

each bounded polygon has a record in the table

landforms and water are polygonal features

layers in a raster model

Layer 1

Layer 2

layers in an vector-based model (1)

Layer 2

Layer 1

layers in an vector-based model (2)

Comparison between raster and vector data models

Quadtree data structure

In this, geographical area is decomposed into four quadrants and the decomposition continues until each quad represents a homogenous unit. The storage requirement of a quadree is much lower than that of a raster having the resolution of the smallest quad element

Quadtree data structure

In this, geographical area is decomposed into four quadrants and the decomposition continues until each quad represents a homogenous unit. The storage requirement of a quadtree is much lower than that of a raster having the resolution of the smallest quad element

THE QUADTREE DATA

STRUCTURE WORKS WITH:

LEVELS

QUADRANTS

HOMOGENEOUS AREAS

N

N

N

N

N

N

N

N

N

N

N

N

N

N

Quad trees

advantages : - computation of standard region properties is easy

- variable resolution and hence less storage requirement

disadvantages : - translation invariant (two regions having same size

and shape can produce different quadtrees.

- cannot split into parts

Topology

Topology is a branch of mathematics that deals with properties

of space that remain invariant under certain transformations.

Properties : 3 spatial relationships

Containment: Polygons can be defined by set of lines enclose them

Contiguity: Identification of polygons which touch each other or

connect identify contiguous polygons (left or right)

Connectivity: Identification of interconnected arcs, starting point

& end point of network analysis

GIS topology

Topology is a mathematics approach that defines unchangeable

spatial relationships.

When a map is stretched or distorted, some properties change,

Distance

Angles

Relative proximities

Some properties will not change

Adjacencies

Most other relationships, such as "is contained in", "crosses"

Types of spatial objects - areas remain areas, lines remain lines,

points remain points

These unchanged properties are called topological properties.

Topological examples

Network connectivity Polygon adjacency

Topology well-defined

Topology poorly-defined

Importance of topology

Topology enables operations like connectivity and contiguity analysis.

Searching a shortest path

Finding a service area by using a road network

Finding adjacent areas

Topology enables spatial analysis without using a coordinate set,

Apply spatial analysis using topological definitions alone

Major difference from CAD or computer-aided cartography

Topology and GIS analysis

Searching a shortest path

The shortest path from the blue point to the yellow

point is through the red point and then the

orange point (2+1+2.5=5.5 map units).

However, if the topology of the red point is not

defined clearly, which means the two purple

lines are consider as one and the two orange

lines are considered as one, the resulting answer

will be wrong (2+2+2=6 map units).

Finding adjacent areas

The overlapped two polygons have to be

cut into three in order to clearly

defined the spatial topology.

Otherwise there will be difficulties

finding an adjacent polygon of either.

2.5

2 3

2.5

1

2

2

2

Lines: fundamental spatial data model

• Lines start and end at nodes

• line #1 goes from node #2 to node #1

• Vertices determine shape of line

• Nodes and vertices are stored as coordinate pairs

node

node

vertex

vertex

vertex

vertex

• Polygon #2 is bounded by lines 1 & 2

• Line 2 has polygon 1 on left and polygon 2 on right

Polygons: fundamental spatial data model

• complex data model, especially for larger data sets

• “arc-node topology,” used for ArcInfo data sets or defined by rules in the

Geodatabase.

Polygons: fundamental spatial data model

Buffers in GIS

Why buffers are needed?

For proximity analysis.

Examples

Point buffers

Line Buffers

Polygon Buffers

Buffers - Examples Point buffers

Number of households around 5 km of the primary school.

Number of wells that can be contaminated by a chemical factory due to a

possible chemical leakage.

Location of a water abstraction well that does not fall within 5km

distance form a chemical factory.

To assess whether asthma is more prevailing close to a incinerator.

Line buffers

Pollution sources located within the reservation areas of a small stream.

Number of illegal constructions in the reservation area of the railway line

from Point X to Y.

Zones of noise pollution in major roads.

To assess whether crimes are more prominent close to main roads

Polygon buffers

Banks located within 2 km distance from the central business district of

a town.

Number of small water bodies located within 5 km distance from the city

limits.

This presentation has been produced with the help of the resources available

in www