Cartography and Geovisualization

Why cartography?Maps are the principle means of displaying spatial data

Exploration: visualization, leading to conceptualization of patterns and processes.

Communication: convey information and findings that are difficult to express verbally.

The Connected States of America

emerging communities based on their social interactions

communities defined by human networks do not always coincide with administrative boundaries.

Exploration and Communication

Exploration

Confirmation

Presentation

Synthesis

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Cartographic communication

Why cartography?To become a ‘complete’ GIS analyst, you need to become familiar with the basic elements of cartography and, in particular, map design.

http://liam.avenza.com

Maps are not infallible.Maps must “lie” in order to convey information.All maps introduce distortion (3D to 2D):

shape (conformance)size (equivalence)directiondistance

Often mistakes are made, but

sometimes errors are made deliberately (why?).

How do they lie?Simplification: take a complicated feature

and make it simple

Displacement: moving things from their true location

Smoothing: making jagged shapes rounded

Selection: Choosing what to show

Enhancement: causing features to look like we expect,

rather than how they really are

Aggregation: merging features together

Orientation (N/S or arbitrary rotation [to maximize use of page])

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Map design criteriaWhat is the motive, intent or goal of the map?

Who will read the map (the audience)?

How will the map be used: stand alone, in a report, or simply for your viewing?

Real world Conceptualization Measurement & representation Analysis

Interpretation, validation & exploration

What are Map design criteria?

What things / circumstances would require you to design a map differently?

Map design criteriaWhat is the motive, intent or goal of the map?

Who will read the map (the audience)?

How will the map be used: stand alone, in a report, or simply for your viewing?

Real world Conceptualization Measurement & representation Analysis

Interpretation, validation & exploration

Cartographic transformationsThree stages in the transformation of the Earth's surface from

‘reality’ to ‘map’ can be recognized:

Primary: geometric -- map projections

Secondary: semi-geometric -- geoid to ellipsoid(Datums)

Tertiary: generalizationGeneralization is a non-reversible process, and therefore must be carefully considered.

Going from 3-D reality to 2-D cartographic representation requires several transformations. What would they be?

Cartographic transformationsThree stages in the transformation of the Earth's surface from

‘reality’ to ‘map’ are generally recognized:

Primary: geometric -- map projections

Secondary: semi-geometric -- geoid to ellipsoid(Datums)

Tertiary: generalizationGeneralization is a non-reversible process, and therefore must be carefully considered.

Generalization

Generalization has four main components:

Simplification: excluding unwanted, enhancing desired

Classification: reduces complexity (qualitative, quantitative)

Symbolization: implicit or explicit, mimetic or abstract

Induction: logical inference--integration of parts into a whole

Mandates & scale are prime considerations.

What are the main concepts / requirements / processes involved in generalization?

Generalization

Generalization has four main components:

Simplification: excluding unwanted, enhancing desired

Classification: reduces complexity (qualitative, quantitative)

Symbolization: implicit or explicit, mimetic or abstract

Induction: logical inference--integration of parts into a whole

Mandates & scale are prime considerations.

Generalization

Both processes reduce the detail

Simplification Classification

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Topology?

Simplification

The first image: ungeneralized data set, the second: generalized at an 0.1 foot tolerance, the third: generalized at a 10 foot tolerance.

Impact of simplification tolerance

ArcMap’s simplify line

A necessary processas the scale changes

Simplification routinesare available in most

GISystems.

ArcMap’s Generalization toolset

Classification

Number of classes? (4-6 is considered best)

Type

CategoricalNominal

Ordinal

NumericalInterval

Ratio

Classification schemesDividing up data: numerical classification

Exogenous schemesArbitrary schemes (e.g., equal interval)Ideographic schemes (e.g., natural breaks, quantiles)Serial schemes (e.g., standard deviation)Unclassified schemes

You should always explore your data (e.g., histograms) and try different class schemes before settling on one.

Know your data!

When looking at numerical data, what ways of grouping the data can you think of?

Classification schemesDividing up data: numerical classification

Exogenous schemesArbitrary schemes (e.g., equal interval)Ideographic schemes (e.g., natural breaks, quantiles)Serial schemes (e.g., standard deviation)Unclassified schemes

You should always explore your data (e.g., histograms) and try different class schemes before settling on one.

Know your data!

Symbolization components (PGEs)

Can you identify ways in which graphic components can

be varied in order to distinguish different graphic

elements?

(Such as allowing a reader to distinguish different road

classes, different zoning areas.)

Symbolization components (PGEs)

Primary Graphic Elements (PGEs)

In creating symbols, what can you vary?

Is the data quantitative or qualitative?

A useful site that explains these concepts.

PGEs

You must also consider how the spatial primitives (point, line, area) interact with the Primary Graphic Elements (PGEs).

Source: MacEachren 1994 (from Visualization in Geographical Information Systems, Hearnshaw H.M. and Unwin D.J. (eds.). Reproduced by permission of John Wiley & Sons, Ltd.)

Bertin’s graphic primitives, extended from seven to ten variables (the variable location is not depicted) [Info here]

Qualitative data symbolization

Abstract vs mimetic(Implicit vs explicit)

Ternary plots

http://soiltexture.r-forge.r-project.org/

Visual hierarchy

Other cartographicconcerns, such asthe visual hierarchy,are also important.

The proper use oftype is also veryimportant.

Every map must contain some fundamental elements

Depending on the scale, you may or may not need a grid and an inset map.

All maps should be enclosed by a neat line.Title

LegendProjection

Grid

Data Source

Inset map

Map Body

Author

North Arrow

Scale

Map design is an art

It is easy to make a map, but making a great looking map ...requires consideration of all of the elements, and a sense of design.

http://landtrustgis.org/technology/advanced/design

Dasymetric maps

Dasymetric maps use the intersectionof two datasets to obtain a moreprecise estimate of a spatial distribution.

For example, census tracts often containlarge tracts of land whereon peoplecannot live (e.g., parks, industrial areas).

Excluding those areas when determiningstatistics such as population density canmake a significant difference to the values.

Scale and mandates

Reality Abstraction

1: 100 1: 5,000,000

World is flat World is roundWorld is ellipsoidal

Why?

SummaryCartography is both an art and a science.

Maps are fundamental to any GIS project.

Modern advances in GISoftware make it very easy to produce both good and bad maps.

Any map is just one of all possible maps.

Complex maps can be difficult to understand.

SummaryWe have only scratched the surface with respect to the elements of cartography that are important in presenting the results of your GIS-based analyses.

The quality of the map will determine, to a large extent, the reception of your work.

A poorly produced map suggests that the analyses were also poorly handled.

A quality map suggests that the analyses were also done properly and with due care.