Map Projection & Coordinate Systems

ArcView_module_6May 13, 1:30 PM

Outline Map Projection

Coordinate Systems

Setting a Map Projection in ArcView

Manipulating a Map Scale in ArcView

Map Projection Transforming three-dimensional

space onto a two-dimensional map

Map Projection

Curved Earth surface

Flat Map

Projection Types

Map Projection

Projections can be conceptually created by projecting from one geometric shape (a sphere) onto another (a cone, cylinder, or plane) Cylindrical: projects a sphere onto a

cylinder Conic: projects a sphere onto a cone Planar: projects a sphere onto a plane.

Cylindrical Projection

Good for displaying the world

Map Projection

Conic Projection

Good for displaying mid-latitude area such as U.S.

Map Projection

Planar Projection

Good for displaying hemisphere with one focus

Map Projection

Point or Line of Tangency

Point or line of zero distortion Projection distortion increases with

distance from the point of contact

Point for planar projection Line for conic/cylindrical projection

Map Projection

Point or Line of Tangency Cylindrical/Conic projections have

Standard parallel (line of tangency) Central meridian

Planar projections have Reference latitude (point of tangency) Central meridian

Map Projection

Coordinate Systems Defined based on a variety of geodetic d

atums, map projections, units, and reference systems

Coordinate Systems

Datum Used as a reference as in

surveying or mapping Based on the Spheroid (earth

model) Usually referred to as a keyword

(e.g. NAD83, WGS84)

Coordinate Systems

Datum

Coordinate Systems

Spherical vs Planar

Coordinate Systems

Spherical Planar

Dimension

3 2

Projection no yes

LatitudeLongitude

Global vs Local

Coordinate Systems

Global Local

feature Used globally Specific to local area

example GeographicUTM

State PlaneNational Grid

Choosing a Map Projection

depends on Which region to display (e.g. world, north po

le, equator, US) Resolution of the region Geometric properties of the region Purpose of using maps

such that the distortion can be minimized

Setting a Map Projection in ArcView

View Properties menu In ArcView. a view's map projection can

only be set if the map units of the spatial data it contains are decimal degrees

Setting a Map Projection in ArcView

Term definition Map units are the units which the spatial dat

a is stored in Map scale is the relationship between the di

mensions of a map and the dimensions of the Earth

Distance units are the units used by ArcView to report the result of operations (e.g. measurement (measure tool), dimension of shape (draw tool), dimension of selection box (select feature tool))

Manipulating a Map Scale in ArcView