C7

• Data manipulations


  Pre-analysis, needs to be completed before further analysis can be done
• Data preparation


  • Putting data in a useable and compatible format with other data layers
  • The most important part is changing the projection, also known as REPROJECTION
• Most maps (in the US) have already been projected, so when they are digitized, the projection, coordinate system, and datum automatically apply to the digital map

  
• Since the majority of the maps are projected, similar projection was made

  
• Tools for reprojecting data

  • A specific tool within a GIS software
  • ArcView 9.0 (within its toolbox)
  • Blue Marble Geographics (able to make coordinate conversion)

  
• Process of reprojecting the coordinates

  1. Identify the data source file of the map layer to be projected

  2. Identify the current coordinate system and datum

  3. Identify the new coordinate system and datum

  4. Provide a new filename and path to save the new data source

  
• Table query


  A retrieval tool that is an early step in analysis, allowing the user to select a group of records that meet a specified set of criteria
• Table query example


  • Yield point to create the criteria 180 ton/ha
• Table Summaries


  • Summarizing the data statistically by calculating mean, standard deviation or range
  • Combining or calculating new information from current variable using a field calculator
  • Using scripts to complete tasks
  • A technique to join aspatial data with a spatial component
• Statistical summaries example


  • Yield monitoring: Yield point will contain 20,000 or more georeferenced yield points, requiring summarization to make sense of it
• Field calculator


  A tool used in GIS to calculate a value within a database attribute field
• Field calculator example


  • Calculating perimeter distance in feet for a vector polygon with an attribute in meters
• Script


  A set of programming statements that can be entered by the user in ArcGIS, providing instructions for the computer to complete a task
• Table join


  Joining is done to connect the aspatial attribute table with the record of the polygon's spatial table when needed, to save storage space
• Vector map tools


  • Spatial analysis tools for comparing points, lines or polygons
  • Overlays: Placing one vector polygon, line or point on top of another to see relationships
  • Unioning: Merging of two adjacent digital soil maps
  • Merging: Combining polygon features from the same layer
  • Intersecting: Subtracting operation, as opposed to unioning and merging
  • Clipping: Subtracting function, also known as a cookie cutter
  • Queries: Retrieval tools that can be used within a map
  • Spatial join: Joining information from a polygon to points

  
• Raster analysis tools


  • Convert to grid: Works best with polygons or boundaries that already have attribute data
  • Interpolation: Estimating the value for each grid cell based on values of surrounding points
  • Finding distances: Calculating distances or other spatial characteristics
  • Proximity: Creating a continuous grid surface based on proximity to specific objects
• Map calculator


  The ultimate tool for spatial analysis, allowing the user to add, multiply, subtract, and perform many other operations on maps

  
• Map calculator example


  • Calculating differences in yield from one year to the next by subtracting the earlier year's grid cell yield values from the current year's