Copyright, 1998-2013 © Qiming Zhou

GEOG1150. Cartography

Sources of DataSources of Data

Sources of Data 2

Sources of data

Map as a representation of the reality Ground survey and positioning Remote sensing data collection Census and sampling

Sources of Data 3

Map as a representation of reality Spatial data - spatially referenced

objects or phenomena Reality Model construction and selection Selection and construction to a

cartographic representation Map Results in the user’s mental map

Sources of Data 4

The nature of spatial data

The nature of spatial data: from reality (a), via model construction and selection to digital landscape model (b), followed by selection and construction to a cartographic representation towards a digital cartographic model (c), presented as a map (d), which results in the user's mental map (e).

From Kraak and Ormelig, 1996.

realityreality

digital landscape

model

digital landscape

model

digital cartographi

c model

digital cartographi

c model

mapmap

mental map

mental map

drawing code for dots, dashes & patches

model constructiongeographical object selection

select and constructcartographic representation

medium output

areageometryattributes

pointsgeometryattributes

linesgeometryattributesx

y

z

Sources of Data 5

Geographical objects

The representation of geographical objects in a (digital) environment as (a) points, (b) lines, (c) areas and (d) volumes.

From Kraak and Ormeling, 1996

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1-D and 2-D objects

The dimensionality of geographical objects – 1-D (inset map) and 2-D.

From Kraak and Ormeling, 1996

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3-D objects

The dimensionality of geographical objects – 3-D.

From Kraak and Ormeling, 1996

Sources of Data 8

4-D objects

The dimensionality of geographical objects – 4-D/time.From Kraak and Ormeling, 1996

before after

18 May 1980

Sources of Data 9

Ground survey and positioning Geodesy - study of the shape and size of the

earth. The earth is so large that its curvature is

relatively insignificant at the local scale. Thus, we may use plane geometry instead of

spherical geometry for plane survey.

plane

sphe

re

Sources of Data 10

Surveying

The aim of surveying is basically to define the location of a point.

Since location is a relative rather than absolute concept, surveyors determine new positions with respect to an existing reference feature.

The geodetic control points provide the frame of reference for surveying.

Measurement of distance and angles based on the Euclidean geometry.

Sources of Data 11

Measuring distance

Mechanical aids: measuring rods, flexible chains and ruled measuring tapes Physical limitations

Electronic distance measuring (EDM) instruments: laser beam or radio waves Line of sight

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Laser distance measuring

Laser beams and radio waves can be used to determine distances between electronic distance measuring instruments with great accuracy.

From Robinson, et al., 1995

A laser distance measurer

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Measuring direction

Direction is defined as angular deviation from a baseline True north - direction to the north pole Magnetic north pole: > 1600 km south of the true

north pole and changing Magnetic declination - local difference between

the true and magnetic north Compass deviation - unpredictable error in

compass readings Compass, optical sighting instruments,

gyrocompass, radio compass

Sources of Data 14

A theodolite

By combining optics with a bubble level and vertical degree circle (a circular protractor ruled in degrees), surveyors could measure horizontal angles as well as vertical angles. The resulting instrument was called transit, which evolved into the modern theodolite.

Robinson, et al., 1995

Sources of Data 15

Traditional survey methods Finding horizontal position

Traverse Triangulation Trilateration

Finding vertical position Differential leveling Trigonometric leveling

Using a transit or theodolite

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Some basic theorems

A

B

C

A(x1, y1)

B(x2, y2)

C(x2, y1)

X

Y

A

C

B

X

Y

ab

c

X

Y

A

C

B

ab

c

Trigonometric Functions

b

aA

c

bA

c

aA tancossin

Pythagorean Theorem22222 bacbac

Distance Theorem

2122

12 yyxxd

Law of Cosines

Cabbac

Baccab

Abccba

cos2

cos2

cos2

222

222

222

Law of Sines

B

b

A

a

C

c

sinsinsin

Sources of Data 17

Traverse

The traverse method involves determining the location of an unknown point by making a series of direction and distance measurements.

From Robinson, et al., 1995.

(Measured angles and distance)

Sources of Data 18

Triangulation

Starting with a baseline of known length on the ground, the position of an off-baseline point can be determined by triangulation, which involves measuring the angles to the point to be located from the ends of the baseline.

From Robinson, et al., 1995.

(Measured angles)

Sources of Data 19

Trilateration

Starting with a baseline of known length on the ground, the position of an off-baseline point can be determined by trilateration, which involves measuring distances to the point to be located from the ends of the baseline.

From Robinson, et al., 1995.

(Measured distance)

Sources of Data 20

Differential levelling

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Trigonometric levelling

Acac

aA

sin

sin

Sources of Data 22

Automated survey systems Total-station instruments

Electronic tacheometer Electronic positioning

NAVSTAR (USDOD) global positioning system (GPS)

Fully operational in 1994 24 orbiting satellites (21+3) Positioned in 6 evenly spaced orbital planes Standard position service (SPS) and precise

positioning service (PPS)

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Total station

A total station looks like a normal theodolite but it has a microcomputer for measuring and recording, as well as laser-beam device for distance measuring.

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Global Positioning System

A Global Positioning System (GPS) receiver that can be used in the field as a hand-held instrument or connected to the computer with digital maps as field navigation system.

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Remote sensing data collection Electromagnetic radiation (EMR)

Electromagnetic wave Absorption and reflection

Aerial photography Panchromatic film (0.3 - 0.7m) Aerial photograph geometry

Electronic imaging devices Satellite images

Sources of Data 26

Vis

ible

UV

Infr

are

d

Sun’s energy (at 6000°K)

Earth’s energy (at 300°K)

0.3m 1m 10m 100m 1mm 1m

Wavelength

En

erg

y

(a) Energy sources

0.3m 1m 10m 100m 1mm 1m

Wavelength

Human eye

Photography Thermal IR scanners

Electro-optical sensors Passive microwave

(c) Common remote sensing systems

Imaging radar

0.3m 1m 10m 100m 1mm 1m

Wavelength

0%

10

0%

Tra

nsm

issi

on

(b) Atmospheric transmittance

Energy absorbedand scattered

The electro-magnetic spectrum

Sources of Data 27

B/W airphoto

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Natural colour airphoto

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Colour infrared airphoto

Sources of Data 30

Panchromatic satellite image

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Multi-spectral satellite image

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Census and sampling

Census - identify and record all members of a population.

Geocoding - the practice of attaching locational information to census data. Entity focus - vector and raster

geocoding. Aggregation.

Sources of Data 33

Vector geocoding

Coordinates are used to define the location of point, line, area and volume features in vector geocoding.

From Robinson, et al., 1995

POINT

(X, Y)

P1(x1, y1)

P2(x2, y2) P1(x1, y1)

P2(x2, y2)

P3(x3, y3)P4(x4, y4)

P5(x5, y5)

x

y

z

P1(x1, y1, z1) P2(x2, y2, z2)

P3(x3, y3, z3)

P4(x4, y4 , z4)P5(x5, y5 , z5)

P6(x6, y6, z6)

P7(x7, y7, z7)

P8(x8, y8, z8)

Sources of Data 34

Raster geocoding

Pixels are used to define the location of geographical entities in raster geocoding.

After Robinson, et al., 1995

1 2 3

1

2

3

n

m

(m, n)

Line

AreaPoint

COLUMNS

RO

WS

Sources of Data 35

Spatial sampling

To make observations at a limited number of carefully chosen locations that are representative of a distribution

Size of sample - dependent upon the nature of distribution

Sampling units - points, lines (transects) and areas (quadrats)

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Sampling Units

Line (Transect) sample

Area (Quadrat) sample

Point sample

Spatial sampling is performed using either point, line or area units, or some combination of these geometric forms.

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Sampling Strategy

Spatial distribution Clustered, random and uniform distribution

Sampling strategy Random Systematic Stratified

Sampling theorem - a sampling interval should be less than half the size of target features in a distribution

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Sample scatter

Sample scatter is usually described in terms of deviation from randomness, with clustering at one extreme and uniformity at the other.

From Robinson, et al., 1995

Clustering Random Regularity

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Stratification

Sampling based on stratification is highly efficient, because it takes advantage of what is already known about the distribution being sampled.

From Robinson, et al., 1995

Forest Type Survey

High

Medium

Low

Sample site

Vegetation diversity

Sources of Data 40

Sampling intervalPeriod

Sampling Interval

Am

plitu

de

According to the sampling theorem, the sampling interval needs to be less than half the size of target features in a distribution.

Robinson, et al., 1995