GEOG 370 Christine Erlien, Instructor Map Basics GEOG 370 Christine Erlien, Instructor

Map Basics Maps as a language Symbolization Scale Simplification/generalization Grid systems Projections

Value of Maps Way to record & store information Way to analyze locational distributions & spatial patterns Method of presenting information & communicating findings

Value of Maps

Graphicacy Understanding graphic devices of communication Why? Maps Charts Diagrams Why? Understanding usage of graphic devices increases our abilities Describing spatial phenomena Making decisions

Maps Model of reality, not a miniature version Media for delivering geographic information Target audience determines level of abstraction, map scale, symbology

Maps as Models: A paradigm shift in cartography Communication paradigm -> analytical paradigm Communication paradigm Traditional approach to mapping Map itself was a final product Communication tool Limits access to original (raw) data

Maps as Models: A paradigm shift in cartography Analytical paradigm Maintains raw data in computer Display is based on user’s needs Transition ~ early ’60s Advantage:

Cartographic abstraction & generalization Selection Classification Simplification Symbolization

Selection Decisions about Area to be mapped Map scale Map projection Data variables Data gathering/sampling

Classification Organizes mapped information Qualitative or quantitative Qualitative: Spatial distribution of nominal or ordinal data Quantitative: Spatial aspects of numerical data

Classification of interval/ratio data Dividing data into categories Natural breaks Quantile breaks Equal intervals Standard deviation

Classification of interval/ratio data Natural breaks Imposed Fractions/multiples of mean income levels Rainfall thresholds that support different vegetation types (e.g., arid, temperate) Calculated by software

Classification of interval/ratio data Quantile breaks Predetermined number of classes Equal # observations in each class 5 classes: good for uniform distributions Limitation: Potentially misleading Numeric size of each class rigid  Numerically similar values may be in different classes Wide-ranging values may be in same class

Classification of interval/ratio data Equal intervals Range between lowest & highest values divided equally among the number of classes

Classification of interval/ratio data Standard deviation Distance of observation from mean GIS calculates mean value & generates class breaks in s.d. measures above & below Using 2-color ramp helps emphasize values

From Longley et al. Geographic Information Systems and Science

Generalizing features From How To Lie with Maps, M. Monmonier

Symbolization http://www.colorado.edu/geography/gcraft/notes/cartocom/cartocom_f.html

Map Types Reference maps Thematic maps Require conformity to standards Examples: USGS topographic maps, navigation charts Thematic maps Cartographer has control over map design Ex: Spatial distribution of variable

Thematic map types: Dot distribution Dots, other small point symbols Dot will represent a set number of a particular feature If nominal symbols are used, will not vary in size. Why?

http://www.unl.edu/nac/conservation/atlas/Map_Html/Demographics/National/Minority_Operated_Farms/1997.htm

http://www.cdc.gov/hiv/graphics/images/dotmaps/83aids.htm

Dot distribution: nominal point symbols

Thematic Map Types: Prop. symbol Proportional Symbol Graduated point, ordinal line symbol Size of symbol proportional to size of data value For areas  color, pattern

Thematic map types: Proportional dot http://goliath.frostburg.edu/rpotts0/ProportionalCircleMapB.jpg

Thematic map types: Ordinal line http://clerk.ci.seattle.wa.us/~ordpics/115137At10TRFigA4.gif

Thematic map types: Ordinal area

Thematic Map Types: Choropleth Subdivisions are preexisting units Example: Census tracts; county, state, national boundaries Average value for areal unit is calculated & symbolized Generally ratio values Example: Population density, yield/acre, average income

http://personal.uncc.edu/lagaro/cwg/color/Choropleth-5Good.gif

Principles of map design Visual variables Jacques Bertin, 1967 System for representing information based on the visual properties & arrangement of graphic symbols

Bertin’s visual variables Hue: Colors perceived Value: Lightness/darkness Saturation: Intensity/purity

Major Map Elements Necessary components of a typical map Title Legend: Interpretive key to symbols Symbols: Used to describe features Scale bar North arrow

Major Map Elements Necessary components of a typical map Projection Cartographer Date of production

Map Elements Some elements are used to selectively assist effective communication Neatlines: Used to frame map Inset maps: Close-up view Charts Additional text Note – when might an inset be necessary Example: when mapping the U.S., useful to put Alaska & Hawaii in inset Example: helpful when observations/data are clustered in a small section of the map

Map Elements Legend Scale Credits North Arrow Place name Inset Ground Figure Neat line Border Title Figure: The area of interest (area being mapped) Ground: background

Map Scale Map scale: Ratio between map distance & ground distance large scale map vs. small scale map 1:250,000 > 1:1,000,000 Large scale map  more details Scale-dependent map display in GIS Minimum vs. Maximum map scale

Methods of illustrating map scale Verbal scale Example: 1 inch equals 63,360 inches Easily understood Representative fraction scale Example: 1:250,000 No units necessary  map & ground distance in same units as fraction 63360 inches=5280 ft=mile

Methods of illustrating map scale Graphic scale Measured ground distances appear on map Change with changes in scale of output

Map scale vs. scale generally Large scale study vs. small scale study Large scale study Extensive in scope or scale Small scale study Small area or limited scope In which study scenario will data be collected in more detail? In the sense it is being used here  opposite the meaning of scale in map scale