ch 10 Flashcards
Spatial Joins, overlay types, area-weighted recalculation, union vs intersect
_____ features remain whole
________features are split to create new features, as in the lowest layer shown here
Joined, Overlay
What is a key in table joins? Give an example
A common field used to link two tables into a single table in a table join. STATE_FIPS
When joining, The _____table receives the additional information
The _____table provides the additional information
target , join
What is a spatial join?
A join where the records are matched using a spatial relationship instead of a key field
Spatial join using intersect
Spatial join using proximity
Spatial join using containment
Cardinality of cities and airports
In the cities and airports example, only one airport can be closest to a city
only one airport record is expected to match each city
A one-to-one cardinality is expected
one to one join
no merge rule needed
Cardinality of septics and geology
Geology to septics = septics (many): geology (1)
In the septics and geology example, a many-to-one cardinality is expected
A one to one join works well and no merge rules are needed because only one geology record is expected to match each septic
Cardinality of highways and soils
Soils to Highways = highways (1): soils (many)
Each highway is expected to cross multiple soil units, so a one-to-many cardinality is expected
A one to many join type would create multiple copies of each highway to match every soil unit it crosses, which is not very helpful
A one to one join type with merge rules works well for this problem
Each field from the soils table can be assigned a merge rule to summarize the information from the records that match each highway
Setting up a join (1 of 2)A congressional staffer must provide a list of representatives from districts with at least 10 deaths from earthquakes
He has a feature class of districts and a feature class of earthquakes with deaths and damage information
The desired output table is a list of districts with the representative names and the total number of deaths
Therefore, districts (cd114) is the target layer and earthquakes (quakehis) is the join layer
The records should be matched if the quake touches the district, so intersect is the appropriate spatial operator
The required output fields include the district ID, the party, the representative’s name, and the sum of the earthquake deaths
One district can match many quakes, but we want summed values rather than duplicate districts, so a one to one join with a sum merge rule on the deaths field is needed
What is the classic overlay?
Information from both parents is copied to the child polygon from the output table
By splitting features, overlay avoids the one-to-many relationships that plague spatial joins
Describe intersect overlays
Intersect only keeps the areas that overlap
Only the polygon regions within the circles remain in the output.
describe union overlays
Union keeps all areas from both inputs, whether they overlap or not
