Measurement Scales Map Scale Coordinate Systems Copyright Susan McDonald Jampoler 2003

Lecture 5 Page 2 Measurement Scales Nominal Names as labels Cincinnati, New York, Leesburg Ordinal Orders / ranks Large (New York), Medium (Cincinnati), Small (Leesburg Interval Arbitrary start point Value relative to arbitrary origin o F Ratio Absolute zero as origin Angles from zero

Lecture 5 Page 3 Factors to Consider Scale Resolution Accuracy Precision

Lecture 5 Page 4 Map Scale Ratio between distances measured on the map and the corresponding distances measured on the ground Representative fraction (RF) Simple ratio 1:1,000,000 1/1,000,000 No units of measurement Statement scale One inch equals one mile (1:63,360) Bar scale Graphical scale

Lecture 5 Page 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 5 Page 6 1:24,0001:100,0001:250,000 Larger scale, smaller area Smaller scale, Larger area Examples of Scale

Lecture 5 Page 7 Scale Each layer of data comes from a determined scale GIS integrates multiple scales Ability to zoom in and zoom out makes GIS scaleless Must be careful in analysis to recognize original data scales Analysis is only as good as the smallest scale data layer Graphics From: Bruce Davis GIS: A Visual Approach Onward Press, 1996

Lecture 5 Page 8 Resolution Measures the level of detail captured in a map Can be related to map scale Types of resolution Informational scale/resolution Spatial resolution Thematic resolution Temporal resolution

Lecture 5 Page 9 Spatial Resolution Graphic From: Joseph Berry, Spatial Reasoning for Effective GIS, GIS World, 1995 Graphic From: Bruce Davis GIS: A Visual Approach Onward Press, 1996

Lecture 5 Page 10 Thematic Resolution Hierarchical geographic reference systems Township and range Municipal addresses Postal codes Census enumeration areas Insert Figure 2.33 Insert figure 2.35

Lecture 5 Page 11 Thematic Resolution Insert figure 3.8 Insert figure 3.10

Lecture 5 Page 12 Temporal Scale / Resolution Important to applications that include Change Movement Dynamics Resolution Number of times an event is measured or recorded More times measured ~ higher resolution

Lecture 5 Page 13 Latitude / Longitude measured in degrees, minutes, seconds from center of the earth Global Reference System (GRS) Latitude 0 o is at equator Longitude 0 o is at Prime Meridian Planar coordinates x, y coordinates Measurements of length, angle and area are constant across the two dimensions Measurements X > 0 Y > 0 X > 0 Y < 0 X < 0 Y > 0 X < 0 Y < 0 0,0 (Origin)

Lecture 5 Page 14 Storing Latitude and Longitude in GRS 0 o Longitude Prime meridian 0 o Latitude Equator - Longitude(x) + Latitude (y) - Longitude(x) - Latitude (y) + Longitude(x) - Latitude (y) + Longitude(x) + Latitude (y) X YWestEast Washington D.C (West longitude, x) +39 (North latitude, y)