karl hennermann school of environment and development session 2: what you absolutely need to know...

Karl HennermannSchool of Environment and

Development

Session 2: What you absolutely need to know

about spatial data

Geographic Information Systems

Contents

I. Defining GISII. The world is a set of layersIII. Vectors and rasters – representing real world

featuresIV. Where am I? Coordinate systemsV. Making maps: cartographic projectionsVI. Challenges and constraints for GISVII. Q&A

Karl Hennermann, 13-03-2013

Defining GIS

GIS is not a software product.


Definition I: GIS is…

A computer system capable of holding and using data on geographical objects

ESRI (1997): Understanding GIS. The ARC/INFO method.


“... geographical objects”


“...data on geographical objects”

Location, location, location

20°E 40°E

60°E55°N

Longitude

La

ti tu

de

20°W40°W

90°N

100°E80°E

Eq

0° 60°E

20°N

40°N

60°N

80°N

60°

55°

90°S

Reference Meridian


“...data on geographical objects”

School locationsName Pupils X Y

Escuela comunitaria 50 -331190.2532 1656981.1846

San Marco 300 -325944.6701 1646684.2992



Santa Barbara 220 -335350.5207 1667812.8615

? 50 -341766.6793 1663579.5197

Colegio comunitario 130 -328868.216 1660867.5351


San Sebastian 60 -327434.1567 1662615.3295

Colegio comunitario 700 -333101.5578 1660735.2432

Santa Maria 80 -322055.1816 1667283.6938

(-324072;1667468), (322317;1665019), (-321993;1661876), (-323010;1660028), (-324211;1659751), (-324396;1660305)

Flooded area


Definition I: GIS is…

A computer system capable of holding and using data on geographical objects



Definition II: GIS is…

An organised collection of computer hardware, software, geographical data, and personnel designed to efficiently capture, store, update, manipulate, analyse, and display all forms of spatially referenced information.



“...hardware, software, geographical data, and personnel to capture, store, update,

manipulate, analyse, and display...“

Process view

Data Collection

Pre-processing

Data Storage & Management

Analysis

Product Generation (maps, reports)

Architecture view

Hardware

Software

Geospatial data

Personnel & Skills


So, what is GIS about?

• GIS is not a software product.

• GIS is about the methods / techniques of analysing data spatially or geographically

• You do not have to use GIS software for work to count as geographical analysis

• The software simply allows these methods to be carried out efficiently


Contents

I. Defining GISII. The world is a set of layersIII. Describing the real world - vectors and rastersIV. Where am I? Coordinate systemsV. Making maps: cartographic projectionsVI. Challenges and constraints for GISVII. Q&A


The world is a set of layers


Jones, Christopher (1997): Geographical Information Systems and Computer Cartography. Addison Wesley Longman.p30

Contents



Describing the real world - vectors


File

Image (c) Google

ID Shape Land use Priority

15(546518; 5322562) ; (499780; 5289643), (505023; 5275120); (552327; 5329340)

Residential 3

14(505023; 5275120); (552327; 5329340); (543336; 5356035)

Industrial 1

34 … Water 485 … Residential 1… … … …

14

15

34

853

17

22

18

44

Describing the real world - vectors


Image (c) Google

ID Shape Name Last checked5 546518; 5322562 Booth Street W 13/03/2011

17 499780; 5289643 Booth Street E 14/01/201312 505023; 5275120 Stretford Road W 05/05/201213 552327; 5329340 Stretford Road E 21/09/2013… … … …

Bus stops(Point)

ID Shape Land use Priority

15(546518; 5322562) ; (499780; 5289643), (505023; 5275120); (552327; 5329340)

Residential 3

14(505023; 5275120); (552327; 5329340); (543336; 5356035)

Industrial 1

34 … Water 485 … Residential 1… … … …

Land use(Polygon)

ID Shape Name Ownership

45(553295; 5326158); (540847; 5333489)

Booth Street public

4(546641; 5273736); (512907; 5283972)

Oxford Road private

6(546518; 5322562) ; (499780; 5289643), (505023; 5275120);

Wilmslow Road public

10(505023; 5275120); (552327; 5329340);

Stretford Road public

… … … …

Roads(Polyline)

Describing the real world - rasters


Logical Data Model1: Green space2: Water body3: Residential4: Industrial5: ...

32 512125 5317265 100 1001,1,1,1,1,1,2,1,1,1,1,1,4,4,1,1,2,1,1,1,4,4,4,4,1,2,1,1,1,1,4,1,1,1,2,1,3,1,1,1,4,4,4,2,1,3,3,3,1,1,3,3,4,2,1,3,3,3,3,1,3,3,2,4,4,3,3,3,3,3,3,2,4,4,4,3,3,3,3,3,2,4,4,4,4,3,3,3,3,3,EOF

File1 4 4 1 2 11

4 3 3 3 33

3 3 3 33

1 1 1 1 11

3 3 3 33

1 12

3 3 33

4 1 2

1

1 1

4 4

4 4

11

2

1

1

1

4

1 1 1 1

1 1

3 1 1

13 3 3 1

4 4 1 1

1 1 1 2

4 4 4 2

3 3 4 2

3 3 2 4

2

3 2 4

4

4

4

1

4 44

1

1

Image (c) Google

Contents



Geographic Coordinate Systems(use on spheres and with GPS)

20°E 40°E

60°E55°N

Longitude

La

ti tu

de

20°W40°W

90°N

100°E80°E

Eq

0° 60°E

20°N

40°N

60°N

80°N

60°

55°

90°S

Reference Meridian


The most common geographic coordinate system is:Decimal Degrees on WGS 1984

In the UK alsoDecimal Degrees on OSGB 1936

The Geodetic Datum

The Measurement Units(almost always DD)

Contents



Making maps: cartographic projections


Y

X

a

b

A method by which the curved surface of the earth is portrayed on a flat surface. This generally requires a systematic mathematical transformation of the earth's graticule of lines of longitude and latitude onto a plane.

ESRI (2010): ArcGIS Desktop Glossary



+

+

++ +

Transverse Mercator



Snyder, John P. (1987), Map Projections – A Working Manual. U.S. Geological Survey Professional Paper 1395. Washington.

The Transverse Mercator projection



There are hundreds of geographic coordinate systems, projections, and projected coordinate systems.Always know what the coordinate system and projection of your data is.

How to make the British National Grid:

Take a spheroid with the OSGB 1936 spec and project it with Transverse Mercator, using the Greenwich meridian as Central Meridian. Then overlay a projected coordinate system, measuring in meters North and East from the Isles of Scilly.

411000 412000 413000

Projected Coordinate Systems(use on maps)


British National Grid:• Units: meters• Reference point is

SW of Isles of Scilly

Northing: 409000(meters north of the reference point)

Easting: 411000(meters east of the reference point)

1000m

408000

409000

Contents



Challenges and constraints

• Data• Data • Data• Cost, arguing that it pays off, and defining

business processes• Multiplication of effort, Interoperability, SDIs

III. Challenges and Constraints


Further reading

• Paul Longley, Mike Goodchild, David Maguire, David W. Rhind (2010): Geographic Information Systems and Science. 3rd Ed. John Wiley & Sons

• Ian Heywood, Sarah Cornelius, Steve Carver (2011): An Introduction to Geographical Information Systems. 4th Ed., Prentice Hall


Thank you


Q&A


karl hennermann school of environment and development session 2: what you absolutely need to know...

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