Spatial Joins Flashcards
Attribute joins are based on a common field. What are spatial joins based on?
Spatial joins are similar to table joins:
There is a source and a destination
User must take into account the cardinality of the feature classes
Spatial joins are not based on a common attribute
Spatial joins are based on a common spatial relationship
The result of a spatial join is a new feature class
List the two spatial relationships on which spatial joins are based?
One feature inside another - containment
One feature closest to another - proximity
What are inside joins? Explain.
features inside a polygon
What are distance joins? Explain.
features closest to other features
An attribute join temporarily appends the fields of the source table to the destination
table. In this respect, how is a spatial join different from an attribute join?
The tables of the participating feature classes are not affected New feature class has fields from both input tables
What determines the geometry of the output feature class in a spatial join?
Output layer has the same geometry type as destination layer
If an airports feature class is joined to a cities feature class, with cities as the destination layer, what type of features, cities or airports, will be contained in the output feature class?
Cities = Points
When using a distance join, what fields, if any, are created automatically?
Distances are given in stored map units
True or false? In an inside join the records of two features will be joined only if one of the
features is completely inside the other feature
True
True or false? In an inside join one of the feature classes must always be a polygon
feature class
True
What is the rule of joining? Explain.
Cardinality rules apply
Must be projected for accuracy
Based on cardinality, spatial joins can be grouped into two categories. What are these
categories?
Simple joins - one to one or many to one
Summarised joins - one to many
What type of spatial joins can be performed if the cardinality is one-to-one or many-toone?
Simple joins
What type of spatial joins can be performed if the cardinality is one-to-many or many-tomany?
Summarised joins
Taking into account cardinality and spatial relationship, spatial joins can be grouped into
four categories. List these categories.
Simple Inside
Simple Distance
Summarised Inside
Summarised Outside
If an airports feature class is joined to a cities feature class (please see the illustration in Figure 1), with cities as the destination layer, what is the cardinality between the two feature classes?
Many to many
In the question above, what type of spatial join would be performed? Please make
reference to the spatial relationship as well as the cardinality. Question 16.
Summarised Distance
In Question 16, assuming that the cities feature class has only one numerical field (POP2007), and that the airports feature class has no numerical fields, how many fields, if any, would be generated automatically as a result of performing the spatial join? Important: Try to answer the question without using the ArcGIS software.
2 numerical fields
one from the OG cities POP2007
+
Distance from the summarised distance
If a cities feature class is joined to an airports feature class (please see the illustration in Figure 1), with airports as the destination layer, what is the cardinality between the two feature classes?
one to many
In the question above, what type of spatial join would be performed? Please make
reference to the spatial relationship as well as the cardinality.
Simple Distance
In Question 19, assuming that the airports feature class has no numerical fields, and that and that the cities feature class has one numerical field (POP2007), how many fields, if any, would be generated automatically as a result of performing the spatial join? Important: Try to answer the question without using the ArcGIS software.
?
What is Euclidean distance (pronounced \yü-ˈkli-dē-ən)? Explain.
he Euclidean Distance tool is used frequently as a stand-alone tool for applications, such as finding the nearest hospital for an emergency helicopter flight. Alternatively, this tool can be used when creating a suitability map, when data representing the distance from a certain object is needed.
What is Manhattan distance?
The distance between two points measured along axes at right angles. eg following roads on a grid system
Why is it not recommended to work with geographic coordinate systems when
performing distance joins?
Using a GCS or inappropriate projection may yield incorrect results
Explain why it is difficult to convert degrees into linear units of measurement such as
kilometres or miles.
Because degrees change depends on where you are on the global, wider at certain middle places on earth and narrow at the poles.
A GIS analyst is performing a distance join between two feature classes. All the feature
classes use a geographic coordinate system. However, the data frame uses a projected
coordinate system with metres as the linear unit of measurement. What will be the units
of measurement in the distance field for the output feature class?
Using a GCS or inappropriate projection may yield incorrect results
. In the question above, what steps should the GIS analyst take to ensure that the units in
the distance field are as accurate as possible?
Project coordinate system
Carry out an Internet search and provide a brief explanation about the State Plane
Coordinate System.
The State Plane Coordinate System (SPS or SPCS) is a set of 124 geographic zones or coordinate systems designed for specific regions of the United States.
What are the two most commonly used map projections in the State Plane Coordinate
System?
Most state plane zones are based on either a transverse Mercator projection or a Lambert conformal conic projection.
A GIS analyst would like to perform a distance join using statewide data for the state of
Kansas. In this case, would it be recommendable for the GIS analyst to use a State Plane
Coordinate System?
No! Must be a system that covers the area specfied.
What is the “one-sixth rule”? Explain
For custom projections, for Albers projections to find standard parellels (Latidtude)
A GIS analyst would like to create a custom conical projection for the state of Tennessee.
She would like to use the one-sixth rule to develop a custom map projection for this state.
List all the required projection parameters she would need to calculate.
Central Meridian
Standard Parellel 1
Standard Parellel 2
Latitude of Origin
Fasle easting and northings
A GIS analyst would like to create a custom map projection for the state of Illinois. She
would like to use the one-sixth rule to develop a custom map projection for this state.
Would you recommend that she uses a UTM projection instead? Explain.
UTM would Longitude degrees cover Illinois
This would be the best option for the least amount of distortion
Does not need to use one-sixth rule
In the question above, would you recommend that the analyst uses a Transverse
Mercator projection? Explain.
Yes, it fits the state as it runs north to south
Albers equal-area conic projection:
a. Who developed the Albers Equal-Area Conic projection?
b. How many standard parallels does it have?
c. What property is best preserved by this projection?
d. In which areas are shape and distance best preserved?
e. What is the maximum range of latitude for this projection?
a. Heinrich C. Albers
b. 2
c. Area
d. between standard parallels
e. 30-35 degrees north to south
Lambert Conformal Conic projection:
a. Who developed the Lambert conformal conic projection?
b. How many standard parallels does it have?
c. What property is best preserved by this projection?
d. In which areas are distance and area best preserved?
e. What is the maximum range of latitude for this projection?
a. Johann Heinrich Lambert
b. 1 (scale factor less than 1) or 2
c. Shape
d. Standard parallels
e. Lat max 35 degrees
Equidistant Conic projection:
a. Who developed the Equidistant Conic projection?
b. How many standard parallels does it have?
c. What property is best preserved by this projection?
d. In which areas are shape and area best preserved?
e. What is the maximum range of latitude for this projection?
a. Claudius Ptolemy
b. 1 or 2
c. Distance - True along the meridians and the standard parallels
d. Standard parallels
e. Lat - 30 degrees max diff
