Copyright © 2006 by Maribeth H. Price 7-1 Lesson 7 Spatial Joins
Copyright © 2006 by Maribeth H. Price 7-2 Outline Learning the purpose and process of doing spatial joins Learning to solve problems with spatial joins
Copyright © 2006 by Maribeth H. Price 7-3 Attribute joins Join tables on common field Joined table Destination tableSource table
Copyright © 2006 by Maribeth H. Price 7-4 Spatial Join Conditions Join two tables based on a common spatial relationship –One feature inside another –One feature closest to another
Copyright © 2006 by Maribeth H. Price 7-5 Spatial join (inside) Join each well record to the record of the geology polygon that it falls inside.
Copyright © 2006 by Maribeth H. Price 7-6 Spatial join (distance) Join each county to the hospital that is nearest it. Each county features gets name of closest hospital and the distance.
Copyright © 2006 by Maribeth H. Price 7-7 Distance join units Distances are given in stored map units Decimal degrees cannot be easily converted to miles or km because the conversion factor varies with latitude Better to use a projected coordinate system… The source data was in a GCS with units of decimal degrees.
Copyright © 2006 by Maribeth H. Price 7-8 Distance joins and the CS Using a GCS or distorted projection may yield incorrect results. Setting the data frame CS is not enough—the source data must be in the right projection. A B C A B C Use source data with a projection that conserves distance! Distance join with GCS sourceDistance join with UTM source
Copyright © 2006 by Maribeth H. Price 7-9 Spatial Join Cardinality Simple joins –One-to-one or many-to-one cardinality Summarized joins –One-to-many or many-to-many The Rule of Joining applies to spatial joins also!
Copyright © 2006 by Maribeth H. Price 7-10 Simple spatial join One-to-one or many- to-one. No ambiguity in assigning fields.
Copyright © 2006 by Maribeth H. Price 7-11 Summarized join Destination table is counties. Source table is schools. Output table gives total schools located in each county. Count field is always generated automatically. User can optionally choose a statistic to calculate, for example, to sum the total number of students in each county.
Copyright © 2006 by Maribeth H. Price 7-12 Which attraction is closest to each hotel? How many attractions are closer to one hotel than another? Point to point joins Distance joins only Simple? or Summarized? Depends on the question being asked… Enforces a one to one cardinality… One to many cardinality…must use summarize
Copyright © 2006 by Maribeth H. Price 7-13 SimpleSummarized Inside Distance Schools Counties Which county is each school in? Hotels Attractions Counties Schools How many attractions are closest to each hotel? Which attraction is closest to each hotel? How far is it? How many schools in each of the counties? Hotels Attractions
Copyright © 2006 by Maribeth H. Price 7-14 How to join Right-click destination table Set Join type to spatial Choose source table Choose join type Specify output file
Copyright © 2006 by Maribeth H. Price 7-15 Setting up a join Sketch the layers How do I want the output layer/table to look? Which is the destination layer? Is this a distance join or an inside join? What is the cardinality? Do I need a simple join or a summarized join?
Copyright © 2006 by Maribeth H. Price 7-16 Example #1 Find all congressional districts that have had more than 10 earthquake deaths.
Copyright © 2006 by Maribeth H. Price 7-17 How do I want the output to look? Which is the destination layer? Is this a distance join or an inside join? What is the cardinality? Do I need a simple join or a summarized join?
Copyright © 2006 by Maribeth H. Price 7-18 Example #2 Develop a pollution risk index for rivers based on the total number of people in the adjacent counties.
Copyright © 2006 by Maribeth H. Price 7-19 How do I want the output to look? Which is the destination layer? Is this a distance join or an inside join? What is the cardinality? Do I need a simple join or a summarized join?
Copyright © 2006 by Maribeth H. Price 7-20 Example #3 Create a table showing the volcano closest to each city in the US
Copyright © 2006 by Maribeth H. Price 7-21 Students can find volcano closest to their city. How do I want the output to look? Which is the destination layer? Is this a distance join or an inside join? What is the cardinality? Do I need a simple join or a summarized join? Or can they? Look at the distances…