660 likes | 825 Views
Gistutorial for Health Lecture 4 Projecting and Using Spatial Data. Lecture 4 Outline. Map Projections Coordinate Systems Map Scales and Units GIS Data Data Sources Linking GIS Layers to Internet Sites. Map Projections. Map Projections and Distortion.
E N D
Gistutorial for Health Lecture 4 Projecting and Using Spatial Data
Lecture 4 Outline • Map Projections • Coordinate Systems • Map Scales and Units • GIS Data • Data Sources • Linking GIS Layers to Internet Sites
Map Projections and Distortion • Map projections produce distortion in one or more spatial properties: • Shape, area, distance, and direction • Specific projections eliminate or minimize distortion
Projection Important • Measurements used to make important decisions • Comparing shapes, areas, distances, or directions of map features • Features and images are aligned New York New York Los Angeles Los Angeles Projection: MercatorDistance: 3,124.67 miles Projection: Albers Equal AreaDistance: 2,455.03 miles Actual distance: 2,451 miles
Projection not Important • Business applications • Not of critical importance • Concerned with the relative location of different features • On large scale maps - street maps • Distortion may be negligible • Map covers only a small part of the Earth's surface
Coordinate Systems • Spherical/Polar • Geographic Coordinate System • Rectangular • State Plane • UTM
Geographic Coordinate System • Latitude and Longitude • Census Bureau TIGER files Geographic Coordinate System Grid
Origin • Longitude (prime meridian) 0 • Latitude (equator) 0
Coordinates Pittsburgh 40 -80
Pittsburgh’s Point • Degrees, Minutes, and Seconds (DMS): • 40°26’2”N latitude • -80°0’58”W longitude • Decimal Degrees (DD) • 1 degree = 60 minutes, • 1 minute = 60 seconds • 40°26’2” = • 40 + 26/60 + 2/3600 = 40 + .43333 + .00055 = • 40.434°
Translated to Distance • World circumference through • the poles is 24,859.82 miles, • so for latitude: • 1° = 24,859.82/360 = 69.1 miles • 1’ = 24,859.82/(360*60) = 1.15 miles • 1” = 24,859.82*5,280/(360*3600) = 101 feet • Length of the equator is 24,901.55 miles
Rectangular Coordinate Systems State Plane Coordinates • Local Governments UTM • US Military Rectangular Coordinate System Grid
400 (400, 300) North (Feet) 200 (100, 200) 0 0 200 400 East (Feet) Rectangular Coordinates • Has all positive Cartesian coordinates in feet, called false eastings and false northings
State Plane Coordinate System • Established by the U.S. Coast and Geodetic Survey (now the National Ocean Survey) • At least one for each state • Rectangular (x,y) coordinates • 125 zones, following state and county boundaries each with its own projection: • Lambert conformal projection for zones with east-west extent • Transverse Mercatorprojection for zones with north-south extent • Cannot have zones joined to make larger regions
Universal Transverse Mercator System (UTM) • NIMA - Military grid system • Based on the transverse Mercator projection • Applied to maps of the Earth's surface extending from the Equator to 84 Degrees north and 80 degrees south latitudes
UTM Zones in the Contiguous United States World is divided into 60 north-south zones, each covering a strip 6° wide in longitude
Dimensionless Map Scales • ratio that relates a unit of measure on a map to some number of the same units of measure on the earth's surface • 1:25,000 • tells us that 1 unit of measure = 25,000 of the same units on the earth's surface • 1” on the map = 25,000 inches on the earth's surface • one meter or one yard or one kilometer or one mile would represent 25,000 meters or yards or kilometers or miles, respectively, on the earth's surface.
Small Scale Map Large Scale Map Large and Small Scale Maps 1:5,000 is largescale 1:50,000,000 is small scale
Map Units Feet or meter is the map unit for many local government GIS applications
Map Units Inch is the map unit for CAD applications
Scale 1:100,000 Scale
GIS Data • ArcInfo Coverages • ArcView Shapefiles • CAD Files • Aerial Photos • Event Files
AAT Arc Attribute Table ARC Arc coordinates and topology BND Coverage minimum and maximum coordinates CNT Polygon centroid table PAL Polygon topology PAT Polygon/Point Attribute Table TIC Tic coordinates and Ids DBF Database Table ArcInfo Coverages
Coverage Attribute Table Polygon Coverages • Area and perimeter automatically calculated Line Coverages • Length automatically calculated
B E 1 2 Pine St. 733 A 734 F C Oak St. 3 4 D G ArcInfo Coverages • Advantages • Many feature types • Polygons share borders • Automatic Area/Perimeter/LengthFields • Disadvantages • Cannot edit in ArcMap
ArcInfo Export files • .e00 export exchange file • ArcCatalog translates into ArcGIS • Creates coverages
ArcView Shape Files • Advantages • heads-up digitizing and editing • less storage/rapid display • can export to CAD • Disadvantages • one feature type • no area or perimeter with new shapefiles
ArcView Shape Files • From 3 to 5 Files • .shp - stores feature geometry • .shx - stores index of features • .dbf - stores attribute data • .sbn and .sbx - store additional indices
CAD Files • Why CAD Drawings? • Better Precision for Digitizing • .DWG / .DXF