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Unit Nine: Georeferenced Data. Data Supported by ArcGIS Geodesy Datum Coordinate Systems Projections ArcGIS and Projections ArcCatalog. In this unit…. Review. GIS’ depict reality only approximately! Required: Reality A model A referencing system

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unit nine georeferenced data

Unit Nine: Georeferenced Data

Data Supported by ArcGIS

Geodesy

Datum

Coordinate Systems

Projections

ArcGIS and Projections

ArcCatalog

In this unit…

review
Review
  • GIS’ depict realityonly approximately!
  • Required:
    • Reality
    • A model
    • A referencing system
    • Methods for referencing data within the referencing system
data supported by arcgis
Data Supported by ArcGIS
  • Several types of data are supported by ArcGIS
    • Shapefile
    • ArcInfo Coverage
    • Geodatabase
    • CAD
    • GRID & TIN
  • ArcGIS uses icons to differentiate.
data supported by arcgis1
Data Supported by ArcGIS
  • Some data is of a complex structure:
    • Coverages ‘expand’

Layers are ‘inside’

data supported by arcgis2
Data Supported by ArcGIS

…or a really complex structure

  • Geodatabases can:
    • Store all other types of data
    • Have “Rules”
    • Support Data models
    • Be stored in MS Access
    • Create hierarchical structure of relationships (data sets and data classes)

geodatabase

coverage

shapefile

spatial reference
Spatial Reference
  • DATUM
  • PROJECTION
  • COORDINATE SYSTEM
  • MAP UNITS
datum a model starting place
DatumA “Model” Starting Place

Datum

is

defined

by...

Ellipsoid Size

Ellipsoid Shape

Location of ellipsoid(relative to Earth)

datum history

Ellipse

Lumpy

Potato

DatumHistory

Sphere

Our idea of the earth’s shape evolved…

datum common datum s
DatumCommon 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

USGS

GPS

slide11
.

Map Projections

projection
Projection

Transverse Mercator

coordinates map units a reference grid

Spherical Coordinates

Planar Coordinates

Coordinates & Map Units: A Reference Grid

coordinates are

NH State Plane

map units are

US Survey Feet

Lat-Lon, aka: “decimal degrees”

mapping variables recap
Mapping VariablesRecap
  • The model of the earth on which the data is based?GRANIT DATUM = NAD83
  • The manner in which the data from the model is projected?GRANIT PROJECTION = TRANSVERSE MERCATOR
  • The reference system in which a point is identified/located? GRANIT COORDINATE SYSTEM = NH STATE PLANE
  • The units used in the coordinate systemGRANIT MAP UNITS = US SURVEY FEET
projections in arcgis
Projections in ArcGIS

fyi: Launch components

Tabs – important!

Projection Tools

ArcCatalog

ArcToolbox

projections in arcgis1
Projections in ArcGIS

On-the-Fly Projection

  • Projection for new layers:
    • Defaults to that of Data Frame
    • Data Frame defaults to projection of 1st Layer added
    • On-the-fly DOESN’T change Layer’s original projection
  • To change original projection, use ArcToolbox

Use multiple Data Frames for multiple projections

projections in arcgis2
Projections in ArcGIS
  • Projected Data?
    • ArcGIS still has to know about it
    • Requires “Defining the Spatial Reference”
  • Projection information is stored differently for different types of data
    • Shapefile .prj file
    • ArcInfo Coverage .prj file
    • Geodatabase RDBMS/internal
    • CAD world file
projection info from metadata
Projection Info: from Metadata

Metadata: “Data about data”

    • Documents the data – e.g. all the “variables”
    • Not always included
    • Viewable in ArcCatalog
    • “importable”
  • Metadata Tab for Datum-Projection-Coordinate System Info
    • If it’s projected data, does ArcGIS know it?
metadata
Metadata

Check Out Metadata examples in appendix

  • FGDC metadata – wicked ugly
  • But has a ton of useful info:
    • County codes
    • HYA=0 is quadlines
projection info from properties

clik!

Projection Info: from Properties

View projection info for different files in different ways

coverage

  • Can’t define spatial reference for coverages from here – need ArcToolbox

X

?

defining spatial reference arccatalog

clik!

Defining Spatial Reference: ArcCatalog

View projection info for different files in different ways

shapefile

  • May define spatial reference from here
    • Select “shape” field
    • Click elipsis button

1

2

defining spatial reference arccatalog1
Defining Spatial Reference: ArcCatalog
  • View projection info for different files in different ways

shapefile

    • Two methods for defining:
      • Selecting predefined
      • Importing from other Layer
defining spatial reference arctoolbox
Defining Spatial Reference: ArcToolbox
  • Several flavors of Projection Tools
    • Creating or changing
    • Defining
  • Use if data is un-projected, or needs to be re-projected
  • ACTUALLY CHANGES THE DATA!

X

  • Tells ArcGIS about the projection
  • Doesn’t change data: creates a new file!

Some tools are a little confusing…

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
your turn
Your turn…

Chapter 9: Step 1 through END