Unit Nine: Georeferenced Unit Nine: Georeferenced DataData

In this unit…In this unit…

Data Supported by ArcGISData Supported by ArcGIS

GeodesyGeodesyDatumDatum

Coordinate SystemsCoordinate SystemsProjectionsProjections

ArcGIS and ProjectionsArcGIS and Projections

ArcCatalogArcCatalog

2Unit Nine – Georeferenced DataUnit Nine – Georeferenced Data

ReviewReview

► GIS’ depict realityGIS’ depict realityonly approximately!only approximately!

► Required:Required:

1.1. RealityReality

2.2. A modelA model

3.3. A referencing systemA referencing system

4.4. Methods for referencing data Methods for referencing data within the referencing systemwithin the referencing system

3Unit Nine – Georeferenced DataUnit Nine – Georeferenced Data

Data Supported by ArcGISData Supported by ArcGIS

► Several types of data are Several types of data are supported by ArcGISsupported by ArcGIS ShapefileShapefile

ArcInfo CoverageArcInfo Coverage

GeodatabaseGeodatabase

CADCAD

GRID & TINGRID & TIN

► ArcGIS uses icons to differentiate.ArcGIS uses icons to differentiate.

4Unit Nine – Georeferenced DataUnit Nine – Georeferenced Data

Data Supported by ArcGISData Supported by ArcGIS

► Some data is of a complex Some data is of a complex structure:structure: Coverages ‘expand’Coverages ‘expand’

Layers Layers are are

‘inside’‘inside’

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Data Supported by ArcGISData Supported by ArcGIS

► Geodatabases can:Geodatabases can:

1.1. Store all other types of dataStore all other types of data

2.2. Have “Rules”Have “Rules”

3.3. Support Support Data modelsData models

4.4. Be stored in MS AccessBe stored in MS Access

5.5. Create hierarchical structure of Create hierarchical structure of relationships relationships (data sets and data classes)(data sets and data classes)

ggeodatabaseeodatabase

coveragecoverage

shapefileshapefile

……or a or a reallyreally complex structure complex structure

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Spatial ReferenceSpatial Reference

1.1. DATUMDATUM

2.2. PROJECTIONPROJECTION

3.3. COORDINATE SYSTEMCOORDINATE SYSTEM

4.4. MAP UNITSMAP UNITS

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Ellipsoid SizeEllipsoid SizeEllipsoid ShapeEllipsoid ShapeLocation of ellipsoidLocation of ellipsoid (relative to Earth)

DatumDatumis is

defineddefinedby...by...

Datum

A “Model” Starting Place

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Datum

History

LumpyLumpyPotatoPotato

Sphere

Ellipse

Our idea of the earth’s shape evolved…

Our idea of the earth’s shape evolved…

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Datum

Common Datum(s?)

NAD - 83 (North American Datum - 1983)based on GRS-80 ellipsoid

NAD - 27 based on Clarke 1866 ellipsoid

WGS -84 (World Geodetic System - 1984)based on ellipsoid very similar to GRS-80

GPS

USGS

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Projection

The Basic Idea

11Unit Nine – Georeferenced DataUnit Nine – Georeferenced Data

.

12Unit Nine – Georeferenced DataUnit Nine – Georeferenced Data

Projection

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Coordinates & Map Units:

A Reference Grid

Planar Coordinates

coordinates arecoordinates are

NH State PlaneNH State Planemap units aremap units are

US Survey FeetUS Survey Feet

Lat-Lon, aka: “decimal degrees”Lat-Lon, aka: “decimal degrees”

Spherical Coordinates

14Unit Nine – Georeferenced DataUnit Nine – Georeferenced Data

Mapping Variables

Recap1. The model of the earth on which the data is based?

GRANIT DATUM = NAD83GRANIT DATUM = NAD83

2. The manner in which the data from the model is projected? GRANIT PROJECTION = GRANIT PROJECTION = TRANSVERSE MERCATORTRANSVERSE MERCATOR

3. The reference system in which a point is identified/located? GRANIT COORDINATE SYSTEM = NH STATE GRANIT COORDINATE SYSTEM = NH STATE PLANEPLANE

4. The units used in the coordinate system GRANIT MAP UNITS = US SURVEY FEETGRANIT MAP UNITS = US SURVEY FEET

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Projections in ArcGISProjections in ArcGIS

ArcCatalogArcToolbox

fyi: Launch fyi: Launch componentscomponents

Projection ToolsProjection Tools

Tabs – important!Tabs – important!

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Use multiple Data Frames Use multiple Data Frames for multiple projectionsfor multiple projections

► Projection for new layers:Projection for new layers: Defaults to that of Data Defaults to that of Data

FrameFrame

Data Frame defaults to Data Frame defaults to projection of 1projection of 1stst Layer Layer addedadded

On-the-fly DOESN’T change On-the-fly DOESN’T change Layer’s original projectionLayer’s original projection

► To change original To change original projection, use ArcToolboxprojection, use ArcToolbox

On-the-Fly ProjectionOn-the-Fly Projection

Projections in ArcGISProjections in ArcGIS

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Projections in ArcGISProjections in ArcGIS► Projected Data? Projected Data?

ArcGIS still has to know about it ArcGIS still has to know about it

Requires “Defining the Spatial Reference”Requires “Defining the Spatial Reference”

► Projection information is stored Projection information is stored differently for different types of datadifferently for different types of data

ShapefileShapefile .prj file.prj file

ArcInfo CoverageArcInfo Coverage .prj file.prj file

GeodatabaseGeodatabase RDBMS/RDBMS/internalinternal

CADCAD world fileworld file

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Documents the data – Documents the data – e.g. all the “variables”e.g. all the “variables”

Not always includedNot always included

Viewable in ArcCatalogViewable in ArcCatalog

““importable”importable”

► Metadata Tab for Datum-Metadata Tab for Datum-Projection-Coordinate Projection-Coordinate System InfoSystem Info

If it’s projected data, If it’s projected data, does ArcGIS know it?does ArcGIS know it?

Metadata: “Data about data”Metadata: “Data about data”

Projection Info: from Projection Info: from MetadataMetadata

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FGDC metadata – wicked uglyFGDC metadata – wicked ugly

But has a ton of useful info:But has a ton of useful info:► County codesCounty codes

► HYA=0 is quadlinesHYA=0 is quadlines

Check Out Metadata examples in appendixCheck Out Metadata examples in appendix

MetadataMetadata

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View projection View projection info for different info for different files in different files in different waysways

coveragecoverage Can’t define Can’t define

spatial reference spatial reference for coverages for coverages from here – need from here – need ArcToolboxArcToolbox

Projection Info: from Projection Info: from PropertiesProperties

XX??

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View projection info for different files in different ways

shapefileshapefile May defineMay define spatial spatial

reference from herereference from here1.1. Select “shape” fieldSelect “shape” field

2.2. Click elipsis buttonClick elipsis button

Defining Spatial Reference: Defining Spatial Reference: ArcCatalogArcCatalog

11

22

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►View projection info for different files in different ways

shapefileshapefile Two methods for Two methods for

defining:defining:1.1. Selecting predefinedSelecting predefined

2.2. Importing from other Importing from other LayerLayer

Defining Spatial Reference: Defining Spatial Reference: ArcCatalogArcCatalog

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Defining Spatial Reference: Defining Spatial Reference: ArcToolboxArcToolbox

►Several flavors of Projection

Tools 1.1. Creating or Creating or

changingchanging

2.2. DefiningDefining► Tells ArcGIS about Tells ArcGIS about the projectionthe projection

► Doesn’t change data: Doesn’t change data: creates a new file!creates a new file!

► Use if data is un-projected, Use if data is un-projected, or needs to be re-projectedor needs to be re-projected

► ACTUALLY CHANGES THE DATA!ACTUALLY CHANGES THE DATA! XX

Some tools are a little confusing…Some tools are a little confusing…

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One more thing…One more thing…

►You can simplify your world! “Connecting” to

a folder gives you a shortcut

“Connecting” to a web resource or server lets you share data with others

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Your turn…Your turn…

Chapter 9: Step 1 through ENDChapter 9: Step 1 through END