Lecture 4 Cartographic Process

8/12/2019 Lecture 4 Cartographic Process

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LECTURE 4

THE CARTOGRAPHICPROCESS



Cartographic Generalization Concepts

• Map production necessarily involves undertaking

a number of processes which are collectively

described as Cartographic Abstraction.

• This is the process whereby we transformfeatures of the earth onto a map.

• This involves far more than mere or simple

reduction.

• It is an Encoding Process in which the final

product, the map, will become meaningful to the

map user.



Generalization Processes

• They are logical steps or processes required toachieve cartographic generalization.

• They include selection, classification,

simplification/exaggeration and symbolization.

• By these processes, the cartographer attempts to

portray only the essentials of an environmental

or geographical situation which is defined by the

purpose or objective of the map.• In the process, we often and usually eliminate the

visual complexity of the map by simplifying their

outlines through categorizations



SELECTION

• The map is necessarily selective since, unlike the

photograph, we cannot include all aspects of reality of theworld.

• The first logical requirement of map abstraction

therefore is to reduce the complexity of the environment

to a manageable number.by using clearly definedguidelines or thresholds

• The map makers’ first job is therefore to select the

information that will go into the intended map.

• Selection begins by setting thresholds or cut-off points in

terms of information or data to be mapped.

• In this first stage the cartographer is guided by questions

based on the following: where, when, what.



SCALE SELECTION FACTORS

Purpose of the map

Needs of the map user

Map content

Size of mapped area

Maximum font sizeLevel of accuracy required

Etc.



Factors in the Selection Process

• Purpose/objectives: Since there are various types of maps, decisions made in the selection

process will be guided first by the purpose of the map. The topic and variables to be mapped will beguided by

Physical and material aspects of the environment e.g. topography and hydrology, vegetation,

rainfall and humidity, etc

Non-physical or Human aspects, e.g. Traffic flows, crime and disease

• Region to be mapped: The environment we live in is so vast that it is difficult to obtain a precise

overall picture. The factors that will guide us here include locat ion or localit ies of things to becovered e.g. the whole world or part of it, a continent, country, region or province, district or

settlement.

• Time frame: This relates to current data e.g. yearly or monthly, depending on the objectives of the

map as well as relevance to the map user. In Ghana the most recent topographical maps are dated

1970 and 1990.

• Variables to be mapped: What to include depends on the size or scale of the map; purpose and

available information (e.g. maps for sailors will show cliffs in the sea which ships have to avoid; tourist

maps will show routes and tourist attractions.

• Choice of scale: How to go about reducing the size of our environment to fit the map frame

becomes a most important decision: should the map look at a few things nearby or a lot of things far

away? This consideration addresses one of the concepts in cartography, namely scale. Scale may be

defined as the “ratio of distances on a map, to the actual distances they represent on the ground”.





Data Collection Method

Direct field observation using compass, chain

or Global Positioning System (GPS)

Sampling & Indirect or secondary methods forgathering socio-economic data from reports,

censuses, interviews and questionnaires

Remote sensing methods involving the use thecamera at various altitudes, platforms and films.

(GEOG 307 – Remote Sensing and GIS)



Measurement Level • Measurement levels: Qualitative and Quantitative levels.

Qualitative mode: the cartographic data and the symbols for representing

them are merely descriptive, e.g. the position of a road or river. Quantitative mode : things mapped and the corresponding graphic

symbols (points, lines and areas) vary according to numbers or quantities.

• Inventory Scale

Map makers have important choices regarding the strategy used to collect

information to be mapped. These are the population and sample methodology. Population inventory: When this choice is made, every element of the

distribution is taken into consideration, e.g. every tributary of a river,

every city or every small dam

Sample inventory: In this case, only a portion of the distribution or

population is targeted e.g. only selected tributaries or selected cities in the

distribution, or selected small dams

Sample methodology: The sample methodology for obtaining the required

data may be random, systematic, or stratified

• Cost: The execution of mapping operations has obvious cost implications

which can become a very important factor as it may limit the choice of

alternative actions or activities available to the cartographer. As a result, the

cartographer is sometimes in dilemma regarding the need to produce quality

maps at least cost often demanded by clients or map user.



Since maps are the

transformation of thespherical earth or

parts of it onto a flat

medium like a sheet of

paper, there is need to

understand the basis

and characteristics forsuch a transformation

or projections of

surfaces e.g. cylinder,

cone and plane

/azimuth. Perspective

of the mapped areamay also relate to

aerial photographs

which may be

differentiated as

vertical or oblique

photographs.

A head drawn on the

Mollweide projection(top) has been

transferred to Mercator’s

projection with (centre)

and to the cylindrical

equal-area projection

with standard parallels

at 30 (bottom).

Just because the profile

looks most natural on

Mollweide’s projection,

that projection is notnecessarily “better.”

The natural could have

been drawn on any

projection and then

plotted on the others.

Perspective or

projection



Classification

• Robinson et. al. (1978) have defined classification as “ the order ing or

scal ing and grouping of data with a view to br ing relat ive order

and simp l ic ity out of the comp lexi ty of incom prehensib le

di f ferences, inco nsequential di f ferences, or the unm anageable

magnitudes of information”.

It is a grouping process where information selected for mapping is

grouped into a relatively small number of categories in order to have a

meaningful map.

Map makers generally classify as a means of reducing the complexity of

the map information so that, for example, instead of showing individual

trees, we can have the following: Forested areas, Non-forested area,

Grassland

Therefore the map maker’s first duty in classification is to decide the

number of classes, depending on the characteristics of the data.



Classification Criteria/Methods

Point Feature,Line Typification,

Aggregation of Areas, and

Aggregation of Volumes



Point Feature Methods

Fig 4.1 Illustrations of collapsing process in generalization.

Point feature methods

may result in collapsingof several elements or

features.

This results in obvious

loss of dimension of thefeature being mapped.

We may use this

procedure when we must

group or collapseindividual elements and

specify a typical location

for the group



Line Feature

Typification

Figure 4.2 Typification by classification of point, line and area features

Indeed, the same principles can be applied to all categories of maps including flow maps showing volume of air,

vehicular movement or traffic during rush hour and off peak hours to work.

This method is applied

to complex patterns

consisting of individual

features as shown inFigure 4.2.

The process of

typification allows us to

retain the essence ofthe pattern on the

reduced-scale map.



Aggregation of Areas

• This method results in grouping orcoalescing of area units or features.

• It depends on the size of area units being

aggregated and the scale of mapping in

relation to level of detail e.g. land use

classes

(Level I,

Level II,

Level III,





Number of classes

• Depending on how general a viewpoint

a cartographer takes of the situation,

he can decide to group the data into a

number of classes.

• The choice of few classes for mapping

conceals details whilst a large number

of to overcrowding of information of

the map.

Cl li it



Class limits• In determining the number of classes, the map

maker must determine the class limits.

• A key question to be considered would be “what

point can one group end and another one begin?”

• This is determined by the cartographer’s objective

assessment and understanding of the data.

• In an attempt to classify, we can have constant

series of class intervals; variable intervals which

may be arithmetic or geometric; or even irregular

classes as shown in Table 1



Table 1: Class limits.

Constant

Series

Systematically

Unequal Stepped

Irregular/

Variable

1 – 20

21 – 40

41 – 60

61 – 80

81 – 100

Arithmetic

(5n)

Geometric

(5n

)

1 – 10

10 – 15

15 – 18

18 – 30

1 – 5

6 – 15

16 – 30

31 – 50

1 – 5

6 – 30

31 – 156

157 – 782



SIMPLIFICATION & EXAGGERATION

MANIPULATIONS

• When we undertake cartographic simplification, we determine

important characteristics of feature attributes and, in theprocess, maintain these important features and attributes of the

data and eliminate unwanted details. In doing so, we have two

main objectives:

• We must reduce the amount of information to the map maker’sability to portray it legibly at the chosen scale. At this stage, we

must be guided by how much information to include on the map

• We must maintain as far as possible, the essential geographical

characteristics of the mapped phenomenon

• Cartographers use simplification to eliminate unwanted

information. This is done through two major routines i.e.

elimination and smoothing. The overall objective in simplification

is to avoid overcrowding of information on the map.



Simplification/Manipulation

Procedures

• Feature elimination (Eliminating

unwanted features)

• Smoothing details out of boundaries

• Measurement level reduction

• Combining or compacting variables



Elimination routines

• As map scales get smaller and smaller, fewer features

can be represented. Part of the solution is therefore to

select only the features which are necessary to be

portrayed.

• Cartographers achieve this by eliminating some of it

and smoothing (reducing details) of the remaining

feature.

• Scale of mapping is therefore very important as

illustrated in Figure 4.3 (a, b.). Figure 4.3 (a, b,) further

shows the effect of scale on point feature elimination.



Figure: Simplification accompanied by scale

reduction



Figure: Simplification applied to a constant scale



Simplification manipulation

procedure• Simplification manipulation procedure is

applicable to points, areas and all other types of

features as illustrated in the accompanying

figures.• Depending on the scale of the map, the amount

of detail or convenience desired, some features

and very often those smaller than those desired

may be eliminated, e.g. small outliers as lakes,bridges, streams as shown in Figures 4.4, 4.5,

and 4.6.



Confusion?

• To many map users, this procedure may

introduce a source of confusion in map

information but this is for the convenience

of both the map maker and user alike.

• The procedure could equally be applied to

areas by specifying minimum area or sizeor distance to be eliminated or retained.



SCALE LAKES

STREAM NETWORK

LARGE SCALE

MAP

SMALL SCALE

MAP

Figure: Feature elimination, (Lakes & streams).





Smoothing routines

• Instead of eliminating features, cartographers cansimplify a map by smoothing features.

• As is quite evident with linear features, their form may

further be simplified by removing detail from the edgesas illustrated in Figure 4.7

• In digital mapping smoothing may be carried out by use

of smoothing operators and surface models such as

moving averages and contrast stretching.

• Other routines for carrying out simplification include

measurement level reduction.



SCALE COASTLINE WOOD

LARGESCALE MAP

SMALL

SCALE MAP

Map simplification through line smoothing

(Coastline & Woods/Forest)



SYMBOLIZATION METHODS

• Have you ever noticed that some maps are

easier to understand than others? Often the

difference is due to the mapmaker’s choice and

arrangement of symbols and text.

• A map is most effective when its symbols are

easy to distinguish and their meaning is intuitive.

•

• Your choice of symbols and labels will be

influenced by the type of map you are making.

S b li ti



Symbolization

cartographers’ vocabulary• Symbolization, along with selection, classification and

simplification make up the cartographic generalization

process. Symbolization is the graphic coding of the

selected and grouped essential characteristics,

comparative significances and relative positions(Robinson, et al 1978).

• It is the cartographers’ vocabulary; hence it is the

map’s language. As you have seen in Unit 2, the map

user must be able to communicate with thecartographer to get the required information.

Therefore the choice, designing and positioning of

symbols is very important to make the map serve its

purpose.



Meaning and purpose of symbols

• The issue of symbols and their meaning is therefore particularly

crucial in cartography. Since symbols give meaning to the map, it

must be the case then that they have to be carefully chosen,designed and located or represented in order to convey to the map

user adequate and accurate information regarding earth reality.

• The process of creating graphic symbols to represent feature

attribute values of reality is what we call symbolization (Robinsonet. al). The cartographer turns to the symbolization process after he

had applied classification, simplification/exaggeration routines to

features selected for mapping.

• We can therefore refer to symbolization as the use of visual

variables to represent the summarizations resulting from

classification, and simplification/exaggeration. This is the

graphic coding or application of symbols that makes generalization

possible.



IMPORTANT REMINDER

While you can conclude that symbolization is critical to the

success of any map, you must also realize the following: _________________________________________

Good simplification and classification

procedures can be nullified by poor

symbolization

Good symbolization can enhance the

effectiveness of simplification and

classificationGood symbolization can also impart/give an

unwarranted impression of accuracy to poorly

simplified or classified data.



The symbolization problem

• In order to ensure good symbolization,cartographers usually perform two important

tasks before they choose their symbols.

• They must:

• Select ( and possibly change) the

measurement level of the original data

values, and

• Conceptualize the dimension for each

feature they wish to portray





Types of graphic symbols

Cartographic symbols are either graphic orphotographic (colour, hue, grey tones of black

and white). Graphic symbols are commonly

grouped in three main categories according totheir shape:

• Pictorial or descriptive symbols• Geometrical or abstract symbols

• Letter or number symbols







Measurement scale level

• Most symbols connote only qualitative(nominal) or quantitative (ordinal, interval,

or ratio) data.

• While in measurement theory thedistinction between interval and ratio data

is important, this distinction makes little or

no difference in symbolizing features.

• The only way we can portray interval or

ratio scales is to use textual or numerical

annotations to enhance the symbols.



Examples of differentiation of point, line and area feature on a

nominal scale measurement.

POINT LINE AREA



TYPE Qualitative Distinction

Quantitative Distinction

Point Symbols

Line Symbols

Area Symbols

Volume Symbols

R i Q ti



Review Questions

• The map is necessarily selective. Discussthis statement with reference to any

relevant cartographic generalization

process

• Identify and discuss briefly the principal

cartographic generalization processes youwould employ for a major mapping project

in Ghana

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Lecture 4 Cartographic Process