Unit Nine: Georeferenced Data In this unit… ► Data Supported by ArcGIS ► Geodesy  Datum  Coordinate Systems  Projections ► ArcGIS and Projections ► ArcCatalog

Unit Nine – Georeferenced Data 2 Review ► GIS’ depict reality only approximately! ► Required: 1.Reality 2.A model 3.A referencing system 4.Methods for referencing data within the referencing system

Unit Nine – Georeferenced Data 3 Data Supported by ArcGIS ► Several types of data are supported by ArcGIS  Shapefile  ArcInfo Coverage  Geodatabase  CAD  GRID & TIN ► ArcGIS uses icons to differentiate.

Unit Nine – Georeferenced Data 4 Data Supported by ArcGIS ► Some data is of a complex structure:  Coverages ‘expand’ Layers are ‘inside’

Unit Nine – Georeferenced Data 5 Data Supported by ArcGIS ► Geodatabases can: 1.Store all other types of data 2.Have “Rules” 3.Support Data models 4.Be stored in MS Access 5.Create hierarchical structure of relationships (data sets and data classes) geodatabase coverageshapefile …or a really complex structure

Unit Nine – Georeferenced Data 6 Spatial Reference 1.DATUM 2.PROJECTION 3.COORDINATE SYSTEM 4.MAP UNITS

Unit Nine – Georeferenced Data 7 Ellipsoid Size Ellipsoid Shape Location of ellipsoid Location of ellipsoid (relative to Earth) Datumisdefinedby... Datum A “Model” Starting Place

Unit Nine – Georeferenced Data 8 Datum History LumpyPotato Sphere Ellipse Our idea of the earth’s shape evolved…

Unit Nine – Georeferenced Data 9 Datum Common Datum(s?) NAD - 83 (North American Datum ) based on GRS-80 ellipsoid NAD - 27 based on Clarke 1866 ellipsoid WGS -84 (World Geodetic System ) based on ellipsoid very similar to GRS-80 GPS USGS

Unit Nine – Georeferenced Data 10 Projection The Basic Idea

Unit Nine – Georeferenced Data 11.

Unit Nine – Georeferenced Data 12 Projection

Unit Nine – Georeferenced Data 13 Coordinates & Map Units: A Reference Grid Planar Coordinates coordinates are NH State Plane map units are US Survey Feet Lat-Lon, aka: “decimal degrees” Spherical Coordinates

Unit Nine – Georeferenced Data 14 Mapping Variables Recap 1. GRANIT DATUM = NAD83 1.The model of the earth on which the data is based? GRANIT DATUM = NAD83 2. GRANIT PROJECTION = TRANSVERSE MERCATOR 2.The manner in which the data from the model is projected? GRANIT PROJECTION = TRANSVERSE MERCATOR 3. GRANIT COORDINATE SYSTEM = NH STATE PLANE 3.The reference system in which a point is identified/located? GRANIT COORDINATE SYSTEM = NH STATE PLANE 4. GRANIT MAP UNITS = US SURVEY FEET 4.The units used in the coordinate system GRANIT MAP UNITS = US SURVEY FEET

Unit Nine – Georeferenced Data 15 Projections in ArcGIS ArcCatalog ArcToolbox fyi: Launch components Projection Tools Tabs – important!

Unit Nine – Georeferenced Data 16 Use multiple Data Frames for multiple projections ► Projection for new layers:  Defaults to that of Data Frame  Data Frame defaults to projection of 1 st Layer added  On-the-fly DOESN’T change Layer’s original projection ► To change original projection, use ArcToolbox On-the-Fly Projection Projections in ArcGIS

Unit Nine – Georeferenced Data 17 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  GeodatabaseRDBMS/internal  CADworld file

Unit Nine – Georeferenced Data 18  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: “Data about data” Projection Info: from Metadata

Unit Nine – Georeferenced Data 19  FGDC metadata – wicked ugly  But has a ton of useful info: ► County codes ► HYA=0 is quadlines Check Out Metadata examples in appendix Metadata

Unit Nine – Georeferenced Data 20 View projection info for different files in different ways coverage  Can’t define spatial reference for coverages from here – need ArcToolbox Projection Info: from Properties X ?

Unit Nine – Georeferenced Data 21 View projection info for different files in different waysshapefile  May define spatial reference from here 1. Select “shape” field 2. Click elipsis button Defining Spatial Reference: ArcCatalog 1 2

Unit Nine – Georeferenced Data 22 ► ► View projection info for different files in different waysshapefile  Two methods for defining: 1. Selecting predefined 2. Importing from other Layer Defining Spatial Reference: ArcCatalog

Unit Nine – Georeferenced Data 23 Defining Spatial Reference: ArcToolbox ► ► Several flavors of Projection Tools 1.Creating or changing 2.Defining ► Tells ArcGIS about the projection ► Doesn’t change data: creates a new file! ► Use if data is un-projected, or needs to be re-projected ► ACTUALLY CHANGES THE DATA! X Some tools are a little confusing…

Unit Nine – Georeferenced Data 24 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

Unit Nine – Georeferenced Data 25 Your turn… Chapter 9: Step 1 through END