GIS Data Analysis and Output Flashcards
In general terms, what is data analysis? Explain.
The process of extracting information from data
How is spatial analysis different from data analysis in a discipline such statistics or relational databases?
Spatial analysis extracts or creates new information from spatial data
Why are GIS processes such as attribute queries and spatial queries considered to be data
analysis?
Spatial analysis extracts or creates new information from spatial data
What is geoprocessing? Explain
Geoprocessing involves the use of tools to manage and analyze geographic data
What is a map overlay? Explain
Combining two feature classes
What is the difference between geoprocessing and map overlay?
Geoprocessing includes operations
such as clip, erase, union, intersect,
dissolve, etc.
Map overlay functions combine
spatial layers to create a single
output
What are extraction operations? How are these operations different from other map
overlay operations?
Extractions create new output features classes/shapefiles
List two extraction operations that can be used in ArcGIS?
Clip and Erase
What is the fundamental difference between a spatial join and a map overlay?
Spatial joins do not alter the geometry of input feature classes Features don't always fall neatly inside other features You can join the land-use layer to the roads layer: however, the road does not coincide with the land use boundary Also, a summarized join won't work with categorical data A map overlay, such as intersect, forces the road features to split at the land use boundary Each new segment falls inside one land use category The attribute table of output feature class includes a field with the total road lengths in each land use category
What are point-in-polygon overlays? How is the result of a point-in-polygon overlay different from a spatial join?
The point features in the input layer are included in the output layer
Each point receives the attributes of the polygon where it falls
The result is the same as in a spatial join
Example:
Assign each house point the
associated school district with
education statistics
Allow buyers to compare schools
What are line-in-polygon overlays? How is the result of a line-in-polygon overlay different from a spatial join?
The line features in the input layer are included in the output layer
A line is split at every intersection with a polygon boundary
Each line receives the attributes of the polygon where it falls
What are slivers? Explain how they can be prevented.
Slivers Tiny polygons created during geoprocessing Result of slight differences in boundaries Can build up as a result of multiple operations Nuisance for some applications. For example, when calculating statistics It is desirable to prevent slivers when overlaying
Tolerances can be used to reduce
problems with slivers
A GIS analyst is performing a clip operation (polygon-on-polygon overlay), the input layer
has a UTM coordinate system, the clip layer has a geographic coordinate system, and the
data frame has a State Plane coordinate system. What is the coordinate system of the
output feature class?
Input layer
What is a merge operation? Explain.
Combines multiple features classes into a new feature class
. True or false? A merge operation can only be used with feature classes that have the
same geometry type?
True
True or false? A merge operation will fail if the input datasets do not have the same table
structure. Explain.
True
What is the difference between a merge operation and an append operation?
Appends multiple features classes into an existing feature class
When using the append operation, what happens if the schema of the tables in the input
feature classes does not match the schema of the table in the target feature class?
User can specify if the schema (structure) of the
input tables needs to match the target table
If the property ‘Schema Type’ is set to ‘Test’ the
schema must match, otherwise, ‘No Test’ should be
used
What are the results of a dissolve operation?
Aggregates features based on specified attributes
What are the results of a clip operation?
Extracts input features that overlay the clip features
Why is a clip operation compared to a cookie cutter?
beacuse it is….
What are the results of an erase operation?
Removes the features that fall within the erase features layer (Donut cutter)
How is the erase operation similar to the clip operation? How are they different?
erase = inside Clip = Outside
What are the results of a intersect operation?
Produces the geometric intersection of the input features
How are the results of an intersect operation similar to a clip operation? How are they
different?
Output feature class has attributes from all the input feature classes
True or false? In an intersect operation, where all the input feature classes are polygon, it
is possible to obtain lines or points as the geometry of the output feature class.
False
What are the results of a union operation?
Computes the geometric union of the input features
Input feature classes must be polygon
Preserves all the features from the input
feature classes
Output feature class combines all the features
and attributes of the input layers
You are performing a union operation between a layer of horizontal parcels and a layer of vertical parcels, as demonstrated in class. What do the nulls in the attribute table of the output feature class represent?
Not sure, find out
What are the results of a symmetrical difference operation?
Preservers the features of the input feature classes that do not overlap
