Lecture 2 – Map Projection, DatumLecture 2 – Map Projection, Datum

GPS and Digital MapGPS and Digital Map

Everything in Digital – GPS itself is Everything in Digital – GPS itself is relying on digital technologies.relying on digital technologies.

Fast to transfer and processFast to transfer and process

Digital maps can be made faster and Digital maps can be made faster and cheaper, also more accuratelycheaper, also more accurately

Availability of mapping software and Availability of mapping software and hardwarehardware

Digital Map and GPSDigital Map and GPSWhy digital maps are useful for GPS?Why digital maps are useful for GPS?

Finding addresses quicklyFinding addresses quickly To show where are youTo show where are you Locating nearest service centerLocating nearest service center To show driving directions for somewhere To show driving directions for somewhere you want to goyou want to go To correct your GPS data collectionsTo correct your GPS data collections To create mapsTo create maps To help/guide you through the GPS data To help/guide you through the GPS data collectioncollection

Finding Your DataFinding Your Data

Where you can find the data you want?Where you can find the data you want?

Search over internet with google or yahooSearch over internet with google or yahoo

You can also use data finder services – You can also use data finder services – gis.unc.edugis.unc.edu terraserver-usa.comterraserver-usa.com geographnetwork.comgeographnetwork.com

Library, Government Website etc.Library, Government Website etc.

Typical Map DataTypical Map Data

Topographic Maps (Digital Raster Graphics - Topographic Maps (Digital Raster Graphics - DRG)– have contour lines that trace the DRG)– have contour lines that trace the outline of the terrain and show elevation.outline of the terrain and show elevation.

The most popular topographic maps for use The most popular topographic maps for use within the U.S. are made by ___within the U.S. are made by ___

The topo maps that show the most detail are The topo maps that show the most detail are sometimes called quad sheets or 7.5 sometimes called quad sheets or 7.5 minute maps.minute maps.

Typical Map Data (Cont.)Typical Map Data (Cont.)

TIGER – Topologically Integrated TIGER – Topologically Integrated Geographic Encoding and Referencing Geographic Encoding and Referencing data.data.

TIGER data is free (TIGER data is free (www.census.govwww.census.gov))

DLG – Digital Line GraphDLG – Digital Line Graph

Township and Range – has been used since Township and Range – has been used since the 1790s to survey public lands in the the 1790s to survey public lands in the united states. (PLS)united states. (PLS)

Typical Map Data (Cont.)Typical Map Data (Cont.)

MrSID – (Multiresolution Seamless Image MrSID – (Multiresolution Seamless Image Database. It is a Database. It is a file formatfile format (*.sid) (*.sid) developed and patented by LizardTech. developed and patented by LizardTech.

Graphics in SID format are compressed with Graphics in SID format are compressed with a lossless compression algorithm.a lossless compression algorithm.

DOQ – (Digital Orthophoto Quadrangle) are DOQ – (Digital Orthophoto Quadrangle) are aeiral or satellite photography that has aeiral or satellite photography that has been corrected. been corrected.

Typical Map Data (Cont.)Typical Map Data (Cont.)

ESRI’s Map data – shapefile, coverage, ESRI’s Map data – shapefile, coverage, GRID, geodatabase.GRID, geodatabase.

ERDAS Imagine – IMGERDAS Imagine – IMG

AUTOCAD – DXFAUTOCAD – DXF

http://en.wikipedia.org/wiki/GIS_file_formatshttp://en.wikipedia.org/wiki/GIS_file_formats

Where We Are?Where We Are?

Coordinate SystemsCoordinate Systems

A map datum is a mathematical model that A map datum is a mathematical model that describes the shape of an ellipsoid (the describes the shape of an ellipsoid (the earth). Some examples:earth). Some examples:

Clark 1880, 1886Clark 1880, 1886

NAD 27, NAD 83NAD 27, NAD 83

QornoqQornoq

DjakartaDjakarta

WGS84WGS84

World Geodetic System of 1984 (WGS84) World Geodetic System of 1984 (WGS84) based on the GRS ellipsoid – virtually based on the GRS ellipsoid – virtually identical with the NAD83. WGS84’s identical with the NAD83. WGS84’s previous version is WGS72.previous version is WGS72.

Prior to NAD83, the most popular datum in Prior to NAD83, the most popular datum in U.S. was NAD27, based on parameters U.S. was NAD27, based on parameters determined by Clarke in 1866.determined by Clarke in 1866.

These examples are two common world spheroids used today with their values rounded to the nearest meter. For each spheroid, the difference between its major axis and its minor axis is less than 0.34 percent.

Map ProjectionsMap Projections

(a) Azimuthal (b) Cylindrical (c) Conic. Light source positions, also called perspective positions, play an especially important role in planar projections. (Different aspects, such as polar, equatorial, or oblique, will also affect the map

projection)

Map projections distortionMap projections distortion

The conversion of geographic locations from a spherical coordinate system to a flat surface causes distortion. The projection process will distort one or more of the four spatial properties listed below. Distortion of these spatial properties is inherent in any map.ShapeAreaDistanceDirection

The Universal Transverse Mercator The Universal Transverse Mercator Coordinate SystemCoordinate System

UTM projection has been used by several coordinate systems:

• Part of the civilian UTM system – USGS, 1977

• Part of the state plane system (SPC)

• And the military grid

It has been used for mapping:

• Most of United States

• Many other countries

• The planet Mars

State Plane Coordinate SystemState Plane Coordinate System