measurement scales map scale coordinate systems copyright susan mcdonald jampoler 2003
TRANSCRIPT
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
Lecture 5Page 3
Factors to Consider
ScaleResolutionAccuracyPrecision
Lecture 5Page 4
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
Lecture 5Page 5
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)
Lecture 5Page 6
1:24,000 1:100,000 1:250,000
Larger scale, smaller area
Smaller scale, Larger area
Examples of Scale
Lecture 5Page 7
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
Lecture 5Page 8
Resolution
Measures the level of detail captured in a mapCan be related to map scaleTypes of resolution
Informational scale/resolutionSpatial resolutionThematic resolutionTemporal resolution
Lecture 5Page 9
Spatial Resolution
Graphic From: Joseph Berry, Spatial Reasoning for Effective GIS, GIS World, 1995
Graphic From:Bruce DavisGIS: A Visual ApproachOnward Press, 1996
Lecture 5Page 10
Thematic Resolution
Hierarchical geographic reference systems
Township and rangeMunicipal addressesPostal codesCensus enumeration areas
Insert Figure 2.33
Insert figure 2.35
Lecture 5Page 11
Thematic Resolution
Insert figure 3.8Insert figure 3.10
Lecture 5Page 12
Temporal Scale / Resolution
Important to applications that includeChangeMovementDynamics
ResolutionNumber of times an event is measured or recordedMore times measured ~ higher resolution
Lecture 5Page 13
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)