Administrative

Creating GIS Data from Non-GIS Sources

Common sources

Raw Imagery

CAD Files

Digitizing

Addresses

Different sources, different methods

Raw Imagery

1. Georeference (if necessary)

2. Classify (by Color/Spectral Characteristics) or

3. Digitize (aka Trace)
   
   GeoReferencing Imagery
   
   
   
   Note: JPG and TIF images can be directly read into ArcGIS. But by default, they won't have an appropriate coordinate system and won't overlay anything else. (JPEG 2000 and GeoTiff are standard formats that are not always supported but can save coordinate system metadata information along with the image.)
   
   So we need some data with a coordinate system we trust. (Warning: Google Earth, etc. can be *very* imprecise internationally - see error in this image below).
   
   


So, now we have a valid coordinate system, but our image is clearly pretty far from being correctly registered.

The solution? The "Georeferencing Toolbar" (View->Toolbars->Georeferencing). This tool allows you to identify relationships (by clicking on the screen):

• If you identify one corresponding location in each data layer, the software computes a simple shift.
• If you identify more than one location, the software does a more complex transform (linear, or fancier).

CAD Files

Can simply "open" most common CAD files directly in GIS (DXF, DWG, DGN)

For example, from a real world project, here are CAD data for a regional plan as created by Fonatur, the Mexican national tourism/development agency.



Important limits:

"attributes" don't come along, only layer names *therefore you are well-advised to know the layer naming/numbering convention* (and if none - a big messy problem).

objects must be "exploded" in CAD before export

solids must be converted into boundary representations

Common problems / solutions

Drawn "to scale", but often without explicit projection information and not North aligned

Solution 1: layer properties dialog allows specification of transformations



Solution 2: "world files" (*.wld) are simple text files documenting transforms



Why bother with "world files"?!!! Scalability: one world file can be replicated and applied to many CAD documents drawn against the same base.

Digitizing - Creating new (georeferenced) Geometry

Vector Data Model - Requires boundaries with X,Y coordinates

• Old method - large digitizing table with 'puck' on top of paper map
• New method - 'heads up' digitizing on-screen on top of image
• ArcEdit provides a rich assortment of geographic feature creation tools
  • And, is complex and often counter-intuitive
• ArcSketch provides feature creation tools that are much simpler and intuitive
  • But, is not installed with ArcGISeven though freely downloadable
    • From http://www.esri.com/software/arcgis/extensions/arcsketch/index.html
    • Requires Microsoft .Net Framework Version 2.0 (and the ESRI .NET support feature)
• We will demonstrate use of ArcEdit to create a new shapefile of polygons via 'heads up' digitizing on top of one of the orthophotos that we accessed last week from the MassGIS WMS server. (You could just as easily digitize new polygons on top of any other shapefiles that we have used.)
  • You must first create empty shapefile in ArcCatalog
    • Navigate to a writeable directory and choose File/New/Shapefile
    • specify polygon features
    • specify Mass State Plane (NAD83) mainland coordinates
  • Save this empty shapefile with a name such as, newpolys.shp,
  • In an empty Data Frame in ArcMap, add whichever basemap you want to use for digitizing, then add the empty newpolys.shp shapefile. Just be sure that the map layers in the Data Frame are in Mass State Plane, NAD83 meters, coordinates.
    • For example, add the "Massachusetts Data from MassGIS (GeoServer)" Server:

    http://giswebservices.massgis.state.ma.us/geoserver/wms?

    • and select one of these layers:
      • Black and White Orthos (1990s)
      • 2001 Color Orthos
      • 2005 Color Orthos
    • Zoom in to the MIT campus so you can digitize the building footprint of a few buildings:
• Use ArcEdit to create polygons in your new shapefile
  • Turn on the 'Editor' toolbar from View/Toolbar
• Specify newpolys.shp as the file to be edited
• Create a few polygons
• Examine attribute table and figure out how to add additional attributes
• Try out various editing tools to move, snap, and adjust features
• Recognize complexities: overlapped vs. shared boundaries; moving shared points, choosing an appropriate level of detail, handling curves, labeling points, lines, polygons,...

Addresses - Requires 'Geocoding'

What is Geocoding

• Geocoding is a process of creating map features from addresses, place names, or similar textual information based on attributes associated with a referenced geographic database, typically a street network that has address ranges associated with each street segment or 'link' running from one intersection to the next.
• Geocoding typically uses Interpolation as a method to find the location information about an address. 
  • (If the address along one side of a block range from 1 to 199, then Street Number = 66 is about one-third of the way along that side of the block.)
• Data required:
  • Reasonably clean, consistent list of legal addresses (i.e. not too many typos, addresses really exist, etc.)
  • Address range attributes on a linear street network
    • Most commonly from Census
    • More current/cleaner data available from private vendors
• Geoprocessing as a "Service"
  • Basic setup even in desktop ArcGIS
    • First, in ArcCatalog, create "Address Locator", feeding it street network with addresses + parameters
    • Second, in ArcMap,