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Geography 38/42:286GIS 1

Topic 2:Map Basics and Spatial Data

CharacteristicsChapter 1: Chang

Chapter 1: Dent et al.(Chapter 2: DeMers)

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What is a Map?

Map is a (graphic) model

Basic information:1.

2.

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Kinds of Maps

1) General Purpose Maps

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Kinds of Maps

2) Thematic Maps consist of:

1.2.

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Two Types of Thematic Maps

1) Qualitative

2) Quantitative

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Map Types

Mental Tangible (Real) Virtual

Reference Thematic

QuantitativeQualitative

Multi-VariableSingle Variable

Figure 1.3, Dent6

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Map Scale

Amount of reduction Used to calculate:

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Ratio or Fraction

1:50,000 1/250,000

Advantage:

Expressions of Scale

Map Map Real WorldReal World

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Verbal or Written

1 cm = 50 km

1 in = 1 mile

Advantage:

Expressions of Scale

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Linear or Bar Scale

Advantage:

Expressions of Scale

-1

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Scale Conversions

Ratio or Fraction to Verbal or Written

1:50,000 1/250,0001 cm = 50,000 cm 1 cm = 250,000 cm

1 cm = 500 m 1 cm = 2,500 m1 cm = 2.5 km

Convert real world side to largest unit of measure not

resulting in a fraction

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Scale Conversions

Verbal or Written to Ratio1 cm = 50 km

1 cm = 50 km x 1000m/km x 100cm/m1 cm = 5,000,000 cm

1:5,000,000

1 in = 1 mile1 in = 1 mile x 1 mile/63,360 in

1 in = 63,360 in1:63,360

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Scale Conversions

Linear or Bar Scale to Written

1 cm = 500 km

1 cm

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Large vs. Small Scale Maps

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Large vs. Small Scale Maps

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Large vs. Small Scale Maps1:250,000 Small Scale

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Large vs. Small Scale Maps1:25,000 Large Scale

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Effects of Scale

The scale of a map determines the: Area Size Detail Abstraction

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Large Area/Extent1:250,000 Small Scale

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Small Area/Extent1:25,000 Large Scale

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Small Map Size (given the study area)

1:250,000 Small Scale

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Large Map Size (given the study area)

1:25,000 Large Scale

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Less Detail1:250,000 Small Scale

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More Detail1:25,000 Large Scale

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More Abstraction1:250,000 Small Scale

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Less Abstraction1:25,000 Large Scale

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Effects of Scale

Map ScaleLarge Small

Mapped Area LargeSmall

Level of DetailMore Less

Level of AbstractionLess More

After Figure 1.14, Dent et al.27

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Selecting an Appropriate Scale Who decides? Based on what?

THE MESSAGE YOU WANT TO CONVEYAND INTENDED USE OF THE MAP

Which determines (the stuff we already talked about): extent size detail abstraction

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Cartographic Abstraction

What is it?transforming unmapped data into map form

Four processes of generalization:1. Selection2. Classification3. Symbolization4. Simplification

Inevitable loss of data and/or reduction in quality

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Selection

First step in generalization process

Choose data to include/exclude Theme Hydrology

What features?

What attributes?

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Classification

Organization of data

Same data BUT Different Maps 31

Symbolization

Represent objects

Two types :

1)

2)

Scale dependent

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Simplification

Of map features

Scale dependent

Determines level of detail

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Graphic (Map) Communication

Two transformations of map data:

1)

2)

Is the map reader getting the (intended) message?

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Originally published to wide acclaim, this lively, cleverly illustrated essay on the use and abuse of maps teaches us how to evaluate maps critically and promotes a healthy skepticism about these easy-to-manipulate models of reality. Monmonier shows that, despite their immense value, maps lie. In fact, they must.

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Spatial Awareness and GIS

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Spatial Ontologies

Ontology - study of the nature and organization of reality

Spatial ontology - determines how we define the spatial and aspatial properties of the stuff we are interested in

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Points Lines Polygons

GEOGRAPHIC PRIMATIVES – CARTOGRAPHIC ENTITES

Representation is your, or someone's decisionoften scale dependent 38

Representing Spatial Objects

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Representing Aspatial Attributes

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So What?

How data (spatial and aspatial) are represented determines:

1) How they are storedpoint line poly

using raster or vector modelnominal ordinal interval ratio

(text, int, date, single, double)

2) How they can be used (analysis)raster tools or vector tools

shapefiles vs. feature classestypes of statistical analysis

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