Lec_4_Key Propertires of Spatial Data

Key Properties of Spatial Data

Prof. Dr. Sajid Rashid Ahmad

[email protected]

Atiqa Ijaz Khan _ Demonstrator

[email protected]

Thursday, April 13, 2023Institute of Geology, University of the Punjab

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Key Properties of Spatial data

Projection

3D earth into 2D map

Accuracy

How well does the database info match

the real world

Scale

Ratio of distance on a map to the equivalent distance on the ground

Resolution

The size of the smallest feature able

to be recognized


3Projection

• “A map projection is a mathematical model for conversion of locations from a three-dimensional (3D) earth surface to a two-dimensional (2D) map representation.”

• “A map projection uses mathematical formulas to relate spherical coordinates on the globe to a flat, planar coordinates.” (ESRI)

• “It defines a spatial relationship between location on the surface of Earth to their relative locations on a flat map.” (ESRI)

• “It is a set of rules for transforming features from the 3-dimensional Earth onto a 2-dimensional display.”


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• In GIS software, the layers MUST have same coordinate system

in order to overlay and function properly.

Otherwise, the locations will set out the space or mis-matches.


5Coordinate System

• “It is a reference system used to represent a geographic feature within a common geographic framework.”

• It enable datasets to used common location for integration.


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• Coordinate systems enable geographic datasets to use common locations for integration.

• “A coordinate system is a reference system used to represent the locations of geographic features, imagery, and observations, such as Global Positioning System (GPS) locations, within a common geographic framework.” (ESRI)

• Several hundreds of geographic and few thousands of projected coordinate systems are available for use.

• One can define their own custom coordinate system.


7Coordinate Parameters

• Each coordinate system is defined by the following:• Its measurement framework, which is either geographic or planimetric. • Units of measurement:

• typically feet or meters for projected coordinate systems, or, • decimal degrees for latitude-longitude.

• The definition of the map projection for projected coordinate systems.• Other measurement system properties such as a spheroid of reference,

a datum, one or more standard parallels, a central meridian, and possible shifts in the x- and y-directions.


8Types of Coordinate System

• The following are two common types of coordinate systems: • A global or spherical coordinate system such as latitude-longitude. These

are often referred to as geographic coordinate systems.• A projected coordinate system such as universal transverse Mercator

(UTM), Albers Equal Area, or Robinson, all of which (along with numerous other map projection models) provide various mechanisms to project maps of the earth's spherical surface onto a two-dimensional Cartesian coordinate plane.

• Projected coordinate systems are referred to as map projections.


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Geographic

Projected

Coordinate System CS

GCS

PCS

Coordinate System

Geographic System

Planar System


10Geographic Coordinate System (GCS)

• Always measured in: • Degree-Minute-Second (DMS)• Decimal Degree (DD)

• Origin is at:• Where Prime Meridian meets the Equator.

• In GIS:

Longitude Latitude

Positive Values Eastern Northern

Negative Values Western Southern


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Geographic Grid: is a Location reference system for spatial features

on the earth’s surface.

Parallel:• Line of Latitude in N-S

direction.• Similar to Y-values.• Measured From the

Equator.• As from 0-180 degrees.

(0-90)• Taking Equator as

Reference.

Meridian:• Lines of Longitude in E-

W direction.• Similar to X-values.• Measured Along the

Equator.• As from 0-360 degrees.

(0-180)• Taking Greenwich,

England as Prime Meridian.


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13Parallels of latitude

0° latitude

northlatitude

southlatitude

90°N

Equator

LATITUDE


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LONGITUDE

West Longitude

Meridians of longitude 0° longitudePrime Meridian

Greenwich, England


15Projected Coordinate System (PCS)

• “PCS is defined on flat, two-dimensional surface.” (ESRI)

• It is a 2-dimensional planar surface. (ESRI)

• It is designed for flat surface such as printed map or on a screen.

• A PCS inherits the components of a geographic coordinate system and also has:

• Projection: The mathematical transformation used to convert from geographic coordinates to planar (projected) coordinates.

• Parameters: Parameters used in the transformation. These parameters are specific to the projection.

• Units: Linear measurement for coordinates on the plane.


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• The PCS uses two axes: • the x-axis, representing east-west, and • the y-axis, representing north-south.

• They intersect at the origin, (0,0).

• Locations are defined relative to the origin, using the notation (x,y), where x refers to the distance along the horizontal axis, and y refers to the distance along the vertical axis.

• Points below the x-axis or to the left of the y-axis have negative values.


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Universal Transverse Mercator (UTM)


18Universal Transverse Mercator

(UTM)

• UTM has its root back in 18th century, but come to use by WW-2.

• UTM defines two-dimensional, horizontal positions.

• It is divided into 6-degrees longitudinal strips.• The 1st strips starts at ‘International Date Line’. (180° by GCS)

• The zones are numbered from ‘West-to-East’.• So, zone-2 starts at 174° W to 168° W.• And, zone-60 starts at 174° E to Date Line.

• From 80 degree South to 84 degree North.

• It is also divided into 8-degree zones from equator.

• Each zone has Central Meridian, this is the only line that extends from Poles and perpendicular to Equator.


191. On the southwest coast of Norway, grid zone 32V (9° of longitude in width) is extended further west, and grid zone 31V (3° of longitude in width) is correspondingly shrunk to cover only open water.

2. The four grid zones 31X (9° of longitude in width), 33X (12° of longitude in width), 35X (12° of longitude in width), and 37X (9° of longitude in width) are extended tocover what would otherwise have been covered by the seven grid zones 31X to 37X. The three grid zones 32X, 34X and 36X are not used.

UTM - Exceptions


20Accuracy

• “The degree to which a measured value conforms to true or accepted values.” (ESRI)

• “Accuracy can be defined as the degree or closeness to which the information on a map matches the values in the real world.”

• Accuracy is the closeness of results of observations to the true values or values accepted as being true.

• “Accuracy is the degree to which information on a map matches true real-world values.”


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• Accuracy is a measure of correctness.

• Accuracy could be quantified as ‘Tolerance’.

• Example: • The distance between two points might be given as 173 meters plus or

minus 2 meters. These bands are generally expressed in probabilistic terms.


22Types of Accuracy

Absolute

Horizontal

Vertical

Relative

Precession

Or Positional Accuracy

Types of Accuracy


23Types of Accuracy

• The two classes of accuracy used are as follows;

• Absolute Accuracy:• Measure of the location of features on a map compared to their true

position on the earth.

• Relative Accuracy:• Measure of the accuracy of individual features on a map when compared

to other features.


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25Types of Accuracy

Horizontal Accuracy• For map on publication.

• Not more than 10% of X,Y positions of well-defined points must be within given tolerance as measured on the publication scale.

Vertical Accuracy• For contour map publications.

• Not more than 10% of the elevations tested shall be in error by more than one-half the contour interval.


26Vertical ScaleHorizontal Scale


27Web-site

https://www.e-education.psu.edu/geog469/node/253

Visit to play and understand…




28Scale

• “Scales compare a distance measured on the map to the actual distance on the surface of the earth.”

• Scale is the relationship that the depicted feature on map has to its actual size in the real word.

• Scale is the measurement of the amount of reduction a mapped feature has to its actual counterpart on the ground.

• It represent the relationship of the distance on the map/data to the actual distance on the ground.

• It’s a ratio of distance on the map to the distance on the actual distance on the earth’s surface.


29SCALE...!


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• High Details• Small area

• 1:24,00 or larger

Large Scale

• Average• 1:24,00 – 120,000

Medium Scale

• Less Details• Large area• 1:120,000 or smaller

Small Scale

Types of Scale


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Small Scale

Large Scale


32Large Scale vs. Small Scale

Large Scale• Objects are relatively larger in

size.

• With High details objects.

• Covering the Small area.

• High RF factor.• 1:24,000; 1:50,000 etc.• But, smaller denominator.

Small Scale• Objects are relatively smaller in

size.

• With Low details objects.

• Covering the Large area.

• Small RF factor.• 1:250,000; etc.• But, larger numerator.

Don’t Ever CONFUSE it again… !!!


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Ways to Depict Map Scale

Scale

Verbal Scale Written Scale Scale Text

Fractional Scale

Representative Factor R.F.

Graphical Scale Linear Scale Scale Bar


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Representative Scale Scale BarStatement of Scale

Ways to Depict Map Scale


35Resolution

• “Resolution refers to the ability to recognize and distinguish features.” (ESRI)

• “Ability to separate closely spaced objects on an image or photographs.”

• It could be: low, medium, high, or even very high.

• It’s our choice, One single object can be shown in:• 1 pixel, or• 4 pixels.

• It depends upon:• Sensor technology,• Need for sensor, or user,• Distance between satellite and Earth.


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Resolutions

SPATIALSmallest identifiable

area as a discrete object in an image

SPECTRAL No. of frequencies recorded = sensors

TEMPORALTime interval

between measurements


37SPATIAL RESOLUTION


38Important Points

Image is the Pictorial Presentation of Raster. Pixels are called as Picture elements. Size of Pixel gives the Resolution of the image. Smaller the Pixel size Larger will the Resolution. Every Raster is not image but every image is a Raster.


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* Vegetation in Yellowish green, * Vegetation in Red.* Water in Gray, * Water in Black.

SPECTRAL RESOLUTION


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Spectral Resolution

MSS Multi-spectral Bands: 3-14

Hyper-spectral Bands: 24-224


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Example: for satellite in orange’s shade colors

Time

July 1 July 12 July 23 August 3

11 days

16 days

July 2 July 18 August 3

TEMPORAL RESOLUTION


42SPATIAL RESOLUTIONS

NOAA-AVHRR (1100 m)

GOES (700 m)

MODIS (250, 500, 1000 m)

Landsat TM and ETM (30 – 60 m)

SPOT (10 – 20 m)

IKONOS (4, 1 m)

Quick-bird (0.6 m)


43Serial No. Satellites Altitud

e (km) Bands (µm) Multi-spectral (m) Panchromatic (m)

Thermal (m) Purpose

01. Landsat-7 705 0.5-0.9, 2.03-2.3 30 15 60 Scientific, RS

02. Sea WiFS 705 0.40-0.88 1 (LAC), 4 (GAC)* - - Bio-Oceanic

03. SPOT-5 822 0.5-0.73 10 2.5-5 - Scientific/commercial

04. IKONOS 681 0.45-0.9 04 01 - Urban & Rural Mapping etc.

05. Orb-view 480 0.45-0.9 2.4 0.6 - Commercial, Civil Eng., etc.

06. Quick bird 480 0.45 -0.9 2.4 0.6 Climate change, Commercial, etc.

07. Worldivew-2 770 0.45-0.80 1.84 0.5 - Commercial as Google maps, etc.

*LAC: Local Area Coverage*GAC: Global Area Coverage


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30 m resolution and 60 m resolution (thermal), 705 km orbit, 7 bands including thermal infrared, Manhattan, KS. Image, 2000 (USGS-EROS)

LANDSAT (30 m)


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IKONOS (04 m)MSS

SPOT (2.5 m)


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Quick Bird (0.6 m)IKONOS (01 m) (Panchromatic)


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Imagery and their price ranges


48Imagery free of cost

1. http://glcf.umd.edu/

2. http://glovis.usgs.gov/

3. http://www.usgs.gov/pubprod/

4. http://earthexplorer.usgs.gov/

http://glcf.umd.edu/

http://glovis.usgs.gov/

http://www.usgs.gov/pubprod/

http://earthexplorer.usgs.gov/


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Lec_4_Key Propertires of Spatial Data

Education

spherical coordinate

geographic coordinate

custom coordinate system

projected coordinate

reference system

longitudeinstitute of

ninstitute of geology

coordinate systemin