ch 9&10

Question 1

What are Boolean operators and give an example

Answer 1

Boolean operators test pairs of conditions and return true or false used as part of queries
MAJOR = Geography AND GPA≥3.5

Question 2

What is a spatial operator and give an example

Answer 2

Test spatial relationships between features used as part of queries
Cities within 50 miles of a volcano.

Question 3

True or false
Boolean operators have no order of precedence, unlike arithmetic operators

Answer 3

true

Question 4

What are the three basic operators that test spatial relationships (the three spatial operators)

Answer 4

Intersect, contains/within, proximity

Question 5

What is the intersect spatial operator

Answer 5

Test whether features touch

Question 6

What is the contains/within spatial operator

Answer 6

Tests whether one feature is inside of another

Question 7

What is the proximity spatial operator

Answer 7

Tests whether features are within a specified distance of another

Question 8

What is the difference between the contains and completely contains spatial operators

Answer 8

Contains operator permits the feature to lie on the edge of the containing feature completely contains operator does not permit a shared boundary

Question 9

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?

Answer 9

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

Question 10

Give an example of a spatial query

Answer 10

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

Question 11

What is the biggest limitation of spatial queries?

Answer 11

Spatial queries can only select or not select entire features. Isolating just portions of features requires a different tool like clip or intersect

Question 12

What is a buffer and give an example

Answer 12

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

Question 13

What is the purpose of the dissolved tool when working with buffers in spatial queries

Answer 13

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

Question 14

What is the purpose of the clip tool. Give an example of when it would be used

Answer 14

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

Question 15

What is the purpose of the erase tool. Give an example of when it would be be used

Answer 15

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

Question 16

What is the difference between joins and overlay GIS

Answer 16

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

Question 17

What is a spatial join

Answer 17

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)

Question 18

What would happen in a spatial join using intersect to join zoning to parcels

Answer 18

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

Question 19

What would happen in a spatial join using proximity to join airports to cities

Answer 19

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

Question 20

What would happen in any spatial join using containment to join geology to septic tanks

Answer 20

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

Question 21

What is the type of cardinality that cannot be joined

Answer 21

One (target) to many (join)

Question 22

What is the difference between join type and cardinality

Answer 22

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

Question 23

What is one to many join type

Answer 23

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

Question 24

What is a one to one join type

Answer 24

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

Question 25

What is the cardinality of join zones to parcels. there are usually multiple parcels within one zone. What kind of join do we use?

Answer 25

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

Question 26

What is the current cardinality of cities near airports and what kind of Join do we use

Answer 26

A one-to-one cardinality is expected
a one-to-one join works well

Question 27

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

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

First rule, concatenate rule
a new field was created to store a list of values from each soil unit crossed using the concatenate rule

Question 30

What are the two types of overlay? How are they different

Answer 30

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

Question 31

What is the usual goal of the union overlay? Give an example

Answer 31

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.

Question 32

What is typically the goal of intersect overlay? Give an example

Answer 32

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

Question 33

What is the difference between intersect and clip

Answer 33

Intersect joins the attributes, clip does not

Question 34

Spatial Joins, overlay types, area-weighted recalculation, union vs intersect