GIS Data Analysis and Output

Question 1

In general terms, what is data analysis? Explain.

Answer 1

The process of extracting information from data

Question 2

How is spatial analysis different from data analysis in a discipline such statistics or relational databases?

Answer 2

Spatial analysis extracts or creates new information from spatial data

Question 3

Why are GIS processes such as attribute queries and spatial queries considered to be data
analysis?

Answer 3

Spatial analysis extracts or creates new information from spatial data

Question 4

What is geoprocessing? Explain

Answer 4

Geoprocessing involves the use of tools to manage and analyze geographic data

Question 5

What is a map overlay? Explain

Answer 5

Combining two feature classes

Question 6

What is the difference between geoprocessing and map overlay?

Answer 6

Geoprocessing includes operations
such as clip, erase, union, intersect,
dissolve, etc.

Map overlay functions combine
spatial layers to create a single
output

Question 7

What are extraction operations? How are these operations different from other map
overlay operations?

Answer 7

Extractions create new output features classes/shapefiles

Question 8

List two extraction operations that can be used in ArcGIS?

Answer 8

Clip and Erase

Question 9

What is the fundamental difference between a spatial join and a map overlay?

Answer 9

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

Question 10

What are point-in-polygon overlays? How is the result of a point-in-polygon overlay different from a spatial join?

Answer 10

 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

Question 11

What are line-in-polygon overlays? How is the result of a line-in-polygon overlay different from a spatial join?

Answer 11

 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

Question 12

What are slivers? Explain how they can be prevented.

Answer 12

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

Question 13

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?

Answer 13

Input layer

Question 14

What is a merge operation? Explain.

Answer 14

Combines multiple features classes into a new feature class

Question 15

. True or false? A merge operation can only be used with feature classes that have the
same geometry type?

Answer 15

True

Question 16

True or false? A merge operation will fail if the input datasets do not have the same table
structure. Explain.

Answer 16

True

Question 17

What is the difference between a merge operation and an append operation?

Answer 17

 Appends multiple features classes into an existing feature class

Question 18

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?

Answer 18

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

Question 19

What are the results of a dissolve operation?

Answer 19

Aggregates features based on specified attributes

Question 20

What are the results of a clip operation?

Answer 20

Extracts input features that overlay the clip features

Question 21

Why is a clip operation compared to a cookie cutter?

Answer 21

beacuse it is….

Question 22

What are the results of an erase operation?

Answer 22

Removes the features that fall within the erase features layer (Donut cutter)

Question 23

How is the erase operation similar to the clip operation? How are they different?

Answer 23

erase = inside
Clip = Outside

Question 24

What are the results of a intersect operation?

Answer 24

 Produces the geometric intersection of the input features

Question 25

How are the results of an intersect operation similar to a clip operation? How are they
different?

Answer 25

Output feature class has attributes from all the input
feature classes

Question 26

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.

Answer 26

False

Question 27

What are the results of a union operation?

Answer 27

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

Question 28

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?

Answer 28

Not sure, find out

Question 29

What are the results of a symmetrical difference operation?

Answer 29

 Preservers the features of the input feature classes that do not overlap