ch 9&10 Flashcards
What are Boolean operators and give an example
Boolean operators test pairs of conditions and return true or false used as part of queries
MAJOR = Geography AND GPA≥3.5
What is a spatial operator and give an example
Test spatial relationships between features used as part of queries
Cities within 50 miles of a volcano.
True or false
Boolean operators have no order of precedence, unlike arithmetic operators
true
What are the three basic operators that test spatial relationships (the three spatial operators)
Intersect, contains/within, proximity
What is the intersect spatial operator
Test whether features touch
What is the contains/within spatial operator
Tests whether one feature is inside of another
What is the proximity spatial operator
Tests whether features are within a specified distance of another
What is the difference between the contains and completely contains spatial operators
Contains operator permits the feature to lie on the edge of the containing feature completely contains operator does not permit a shared boundary
What are the target and source features/layers when executing a spatial query. In the example counties that contain volcanoes, which is the target and which is the source?
The target layer is the one from which the features will be selected
the source layer is the one that the target features are compared to
in the example, counties are the target layer and volcanoes are the source layer
Give an example of a spatial query
Select counties that contain volcanoes
Select counties that intersect (touch) rivers
Select cities that are within 50 miles of a volcano
Select rivers that intersect Texas
Select counties within 50 miles of a major airport
Select states with borders that touch Nebraska
What is the biggest limitation of spatial queries?
Spatial queries can only select or not select entire features. Isolating just portions of features requires a different tool like clip or intersect
What is a buffer and give an example
A type of spatial query that delineates the area or boundary of the region within a specific distance of a set of features
ring buffers showing the hundred meter drug-free zones around schools
buffers around streams showing where logging is off limits
What is the purpose of the dissolved tool when working with buffers in spatial queries
By default, each feature gets its own buffer and the default buffers often overlap each other so any area calculations are wildly inflated. The dissolved tool is used in order to generate a single, clean buffer region
What is the purpose of the clip tool. Give an example of when it would be used
The click tool works like a cookie-cutter to extract features that lie inside the boundary of another data set
Clip could be used to extract roads that lay inside the boundary of the city limit and remove the parts of the roads that are outside of the city limit
What is the purpose of the erase tool. Give an example of when it would be be used
Erase is very similar to the clipped tool. It also works like a cookie-cutter to extract features but it extracts the features that lie outside of the boundary rather than the ones that lie inside the boundary of another data set
Erase could be used to extraction the roads that lay outside the boundary of the city limit and remove the parts of the roads that are inside the city limit
What is the difference between joins and overlay GIS
Both join and overlay combine the data tables from two sources but they differ in how they treat overlapping features. Joint features remain whole. Overlay features are split to create new features
What is a spatial join
Any spatial join, the records are matched using a spatial relationship instead of a key field. These relationships are some variation of the spatial operators from queries (intersection, proximity, containment)
What would happen in a spatial join using intersect to join zoning to parcels
Parcels is the target table, so a new parcels feature class is created
the zoning record that intersects each parcel is attached to the parcel in the output table
What would happen in a spatial join using proximity to join airports to cities
Cities is the target later so a new feature class (layer) cities is created
each city in the output table contains information from the closest airport
What would happen in any spatial join using containment to join geology to septic tanks
Skeptics is the target so a new septic’s feature class is created
each output septic system is assigned to the record of the geology unit that it falls within
What is the type of cardinality that cannot be joined
One (target) to many (join)
What is the difference between join type and cardinality
spatial join types offer options for how to handle one too many cardinality. Often times a one to one spatial join will be performed on tables with a one to many cardinality
What is one to many join type
A spatial join type used to create multiple copies of the target feature until there enough for each matching record in the join table when handling a one to many cardinality
What is a one to one join type
Multiple matching records in the join table are summarized using a merge rule creating a single summarized record that can be joined to the target feature
What is the cardinality of join zones to parcels. there are usually multiple parcels within one zone. What kind of join do we use?
many (target)(parcels) to one (join)(zones)
*remember that we say cardinality the opposite of the way we say join
multiple Parcels usually lie within a single zone so the expected cardinality is many to one.
A 121 join works well here
What is the current cardinality of cities near airports and what kind of Join do we use
A one-to-one cardinality is expected
a one-to-one join works well
What is the cardinality of highways and soils and how should they be joined. You wish to determine the soil characteristics for each Highway to help plan maintenance based on which segment of the highway overlaps which kind of soil
Soils to highways
cardinality: highways (one) (taget) to soils (many)(join)
1:many
using a one to many joint tape would create multiple copies of each highway to match every soil unit it crosses so instead we should use a one-to-one joint type with merge rules
What kind of merge rules can numeric fields use? In the Highway soil example given example of a merge rule that might be used on a numeric field
Statistical merge rules like mean or sum.
In the example, the clay and slope fields were assigned a mean rules of the each Highway gets the average of the matching records
What kind of merge rules can be used for text or categorical fields? Give an example of how this might be used in the Highway soil example
First rule, concatenate rule
a new field was created to store a list of values from each soil unit crossed using the concatenate rule
What are the two types of overlay? How are they different
Union combines two polygon layers keeping all areas and merging all attributes for both layers whether they overlap or not
Intersect also merges the attributes for two layers but only keeps the areas that overlap between the two layers. Intersect can be used for points lines or polygons
What is the usual goal of the union overlay? Give an example
The usual goal is to combine all of the data and the extent of the data sets is typically the same.
In a union overlayed hazards table it can be queried for combinations of values that are susceptible to geologic hazards for example rock fall hazards in areas of high slope or high competence.
What is typically the goal of intersect overlay? Give an example
The usual goal is to find overlapping areas were certain conditions hold notice suitability analysis
queries are first performed to find the suitable conditions for what a snail habitat requires for example elevation range, limestone, and dense conifers
the selected features are then intersected to find where they overlap to determine the possible areas of a scale habitat
What is the difference between intersect and clip
Intersect joins the attributes, clip does not
Spatial Joins, overlay types, area-weighted recalculation, union vs intersect
