Measurement Scales Map ScaleCoordinate Systems

Copyright Susan McDonald Jampoler 2003

Lecture 5Page 2

Measurement ScalesNominal

Names as labelsCincinnati, New York, Leesburg

OrdinalOrders / ranksLarge (New York), Medium (Cincinnati), Small (Leesburg

IntervalArbitrary start pointValue relative to arbitrary originoF

RatioAbsolute zero as originAngles from zero

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Factors to Consider

ScaleResolutionAccuracyPrecision

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Map Scale

Ratio between distances measured on the map and the corresponding distances measured on the groundRepresentative fraction (RF)

Simple ratio1:1,000,000 1/1,000,000No units of measurement

Statement scaleOne inch equals one mile (1:63,360)

Bar scaleGraphical scale

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Common Map Scales

1:24,000 scale (1” = about 0.4 miles)

1:100,000 scale (1” = about 1.5 miles)

1:250,000 scale(1” = about 4 miles)

1:500,000 scale(1” = about 8 miles)

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1:24,000 1:100,000 1:250,000

Larger scale, smaller area

Smaller scale, Larger area

Examples of Scale

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Scale

Each layer of data comes from a determined scaleGIS integrates multiple scalesAbility to zoom in and zoom out makes GIS scalelessMust be careful in analysis to recognize original data scalesAnalysis is only as good as the smallest scale data layer

Graphics From: Bruce DavisGIS: A Visual Approach Onward Press, 1996

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Resolution

Measures the level of detail captured in a mapCan be related to map scaleTypes of resolution

Informational scale/resolutionSpatial resolutionThematic resolutionTemporal resolution

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Spatial Resolution

Graphic From: Joseph Berry, Spatial Reasoning for Effective GIS, GIS World, 1995

Graphic From:Bruce DavisGIS: A Visual ApproachOnward Press, 1996

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Thematic Resolution

Hierarchical geographic reference systems

Township and rangeMunicipal addressesPostal codesCensus enumeration areas

Insert Figure 2.33

Insert figure 2.35

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Thematic Resolution

Insert figure 3.8Insert figure 3.10

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Temporal Scale / Resolution

Important to applications that includeChangeMovementDynamics

ResolutionNumber of times an event is measured or recordedMore times measured ~ higher resolution

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Latitude / Longitude measured in degrees, minutes, seconds from center of the earth

Global Reference System (GRS) Latitude 0o is at equator Longitude 0o is at Prime Meridian

Planar coordinates x, y coordinates Measurements of length, angle and

area are constant across the two dimensions

Measurements

X > 0Y > 0

X > 0Y < 0

X < 0Y > 0

X < 0Y < 0

0,0(Origin)

Lecture 5Page 14

Storing Latitude and Longitudein GRS

0o LongitudePrime meridian

0o LatitudeEquator

- Longitude(x)+ Latitude (y)

- Longitude(x)- Latitude (y)

+ Longitude(x)- Latitude (y)

+ Longitude(x)+ Latitude (y)

X

YWest East

Washington D.C.- 77 (West longitude, x)+39 (North latitude, y)