Lecture 04 Referencing Data to Real Locations GTECH 361 Lecture 04 Referencing Data to Real Locations

Today’s Content Two types of coordinate systems Geographic Projected

Today’s Objectives name two types of coordinate systems identify components of each type of coordinate system assign coordinate system information to a dataset set display units for a data frame and measure distances on a map explain what a map projection is list the major categories of map projections list spatial properties that may be distorted when different map projections are applied change the map projection for a data frame and describe its effects

Geographic Coordinates Graticule Latitude Longitude Prime Meridian

The Earth’s Shape The ancient Greek’s mathematical harmony Simplest approximation: the sphere

The Earth as an Ellipsoid

Making of an Ellipsoid

The Earth’s Shape

Why Multiple Datums?

Geodetic Datums

Projected Coordinates Flattening the Earth

Origin of X, Y Coordinates

Central Parallel

False Easting/northing

Coordinates in ArcGIS All geographic data have geographic coordinates (lat/lon) Some may have projected coordinates in addition to the geographic ones ArcGIS assigns the coordinate system to a map based on the GCS or PCS of the first dataset loaded Subsequent datasets are converted on-the-fly

Map and Display Units Map units are determined by GCS or PCS GCS in degrees or decimal degrees PCS usually in feet or meters Display units are determined by you They are defined as part of the data frame

(Decimal) Degrees Converting from degrees to decimal degrees Divide each value by the number of minutes (60) or seconds (3600) in a degree Add up the degrees to get the answer

Map Projection Types Cylindrical Conical Planar

Cylindrical Projections

Conic Projections

Planar Projections

Understanding Distortion Distortion cannot be avoided; we have to choose from distortion of Shape Area Distance Direction

Preserving Properties If two properties are to be preserved then one is always direction These properties are incompatible:

Shape Property Conformal Non-conformal

Area Property

Distance Property

Direction Property

Direction Property Mercator with rhumb line or loxodrome Azimuthal map with shortest distance

Tissot Indicatrices

Equatorial (normal) Aspect

Transverse Aspect

Oblique Aspect

Aspects for Planar Projections Polar Gnomic Stereographic Orthographic

Aspects for Planar Projections Equatorial Aspect Gnomic Stereographic Orthographic

Aspects for Planar Projections Oblique Aspect Gnomic Stereographic Orthographic

Aspects for Conic Projections Normal aspect

Polyconic Projection Hassler, 1820s US Coastal Survey

Perspective Position of the light source

Perspectives

Classifying Projections

Classifying Projections Cylindrical straight parallels; straight meridians Pseudo-cylindrical straight parallels, curved meridians Conic partial concentric circles for parallels; straight meridians Pseudo-conic partial concentric circles for parallels; curved meridians Planar Concentric circles for parallels; straight meridians Modified planar No common appearance of parallels and meridians

Choosing a Map Projection Conformal (shape-preserving) maps Topographic and cadastral Navigation Civil engineering Weather

Choosing a Map Projection Area-preserving maps Population density Land use Quantitative attributes

Choosing a Map Projection Scale-preserving maps no map preserves true distance for all measurements Airline distances Distance from epicenter of an earthquake Cost calculations

Choosing a Map Projection

Components of a GCS An angular unit of measure A prime meridian A datum, which includes a spheroid

Planar Coordinate Systems

Cartesian Coordinates Calculate distance A-B

Universal Transverse Mercator UTM zones

UTM Zones .. as seen from the North Pole

UTM Projections Each zone uses a custom Transverse Mercator projection with its own central meridian

Universal Polar Stereographic Fills the holes of UTM in polar regions

State Plane Coordinate System

SPC N-S zones use Transverse Mercator E-W zones use Lambert Conformal Conic Maximal scale error is 1:10,000 NAD27 or NAD83 datum

Public Land Survey System PLS are shown in purple

PLS It is used to locate areas, not points It is not rigorous enough for spatial analysis like the calculation of distance or direction It is not a grid imposed on a map projection (a system invented in a room), but lines measured on the ground by surveyors

PLS Meridians and Baselines

PLS Area Unit Hierarchy

PLS Township Sections A township is divided into 36 sections, each a square mile (640 acres) A section is divided into 160-acre quarters, which can be further divided into halves, quarters, and so on