1. Getting Started with GIS Analysis Module 6
ESRI Virtual Campus
Learning ArcGIS Desktop Training Course
ESRI ArcGIS
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2. Introduction
A GIS analysis involves visualizing and combining geographic data to derive new information.
A GIS analysis may be as simple as looking at a map and discovering patterns in the data
such as clusters of asthma cases close to a heavily trafficked freeway.
Some GIS analyses are very complex and involve many data layers and operations
such as an analysis to predict the spread of a contamination plume and its possible effects on a watershed
Can include many different operations and methods.
All analyses follow a process that includes specific steps
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3. Learning Objectives List the steps in a GIS analysis.
Interpret an analysis plan that includes GIS tools, criteria, and workflow.
Extend a layer attribute table by joining another table to it.
Create and modify a selected set of features using a series of attribute and location queries.
Explain the difference between attribute and location queries.
Examine analysis results through maps, tables, and reports.
Generate a report that presents the results of an analysis.
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4. Analytical Process Usually includes seven steps Define the problem
Define the criteria
Identify the data you need
Plan the analysis
Prepare the data for analysis
Execute the analysis
Examine and present the results
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5. Analytical Process
May need to repeat at least some of the steps in order to refine or adjust analysis
While planning analysis (step 4), an additional feature class is needed, go back and identify another data source (step 3)
Examining analysis results (step 7) leads to criteria modification (step 2) and repeating of the analysis.
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6. Getting Specific First three steps are key
Clearly define the problem to be analyzed
Define the criteria that will direct the analysis
Identify the data you will use
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7. Define the Problem Not always an easy task
Try to describe scope of the analysis in one or two sentences
If broad
Break into several smaller parts that can be individually analyzed
"What sections of beach are most likely to suffer damage in a hurricane?"
Might need to be analyzed in three parts:
What sections of beach have had a high rate of erosion?
What sections of beach are not protected from urban development?
What sections of beach have both high erosion and are unprotected?
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8. Define the Problem GIS analysis doesn't actually solve a problem
Utilizes data and derives information from it
Analysis results
A person (or group of people) uses the information to make a decision
Hopefully solving the problem
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9. Define the Criteria Define what criteria is going to be used
In terms of specific distances, measurements, or attributes
In the previous example
Just how much erosion is a high rate?
Two feet per year?
Five feet per year?
The answer may depend on the purpose of your analysis, a scientific methodology you are following, or the data that is available.
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10. Identify the Data
What feature classes and attributes are needed to find features or locations that meet the criteria?
Beach erosion problem
Beach sampling stations with attributes containing beach erosion rates or measurements
Urban areas or land use zones.
List data that might be needed for orientation or for presentation of the analysis results
i.e. a coastline layer
Investigate metadata
Data source, purpose, permissions, coordinate system, and attribute descriptions
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11. Planning the Analysis Creating an analysis plan
Can prevent mistakes and save time when executing analysis
Additional data may be needed
Test a particular approach or tool
Diagram a plan or tool to identify
Sequence of steps
Specific tool to use at each step
Data required and produced by each tool
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12. Planning the Analysis
Workflow for finding parcels that would be affected by a street widening project
Identifies data layers and GIS tools to be used and shows proper order for entire process
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13. Preparing the Data Identify steps needed to prepare data
Add a field to a table
Edit or update features
Correct data errors
Change or define coordinate systems
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14. Execute the Analysis If planning process was thorough
executing the analysis should be straightforward
Follow the workflow diagram steps
It's always a good idea to perform the analysis using a copy of the data
Especially important if analysis includes processes that change the original feature class, table, or database
i.e. combining feature classes, calculating new attribute values, or adding or removing features
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15. Examine and Present the Results
Doesn't always accomplish the desired results the first time through
Iterative process
Verify results and visually analyze the data produced by intermediate steps as well as the final analysis
When verifying results, consider:
Are the results what you expected?
Does it appear that the process you performed worked correctly?
Evaluate results in relation to the original analysis goal
Do the results answer your geographic question?
Is this new information valid or useful?
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16. Examine and Present the Results
Draw conclusions from analysis results
Produce an output to share with others
On a land use planning project
Create and print one or more maps that can be reviewed by the planning commission or the general public
Analysis of a lake's water quality
Create maps, graphs, and tabular reports
Analysis results may
suggest that a decision or action is needed
raise new questions
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17. Examine and Present the Results
Results of a water quality analysis
Presented in a map and graph
Map shows water quality sampling station locations
Graph shows water quality trends
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18. Exercise
Define a Problem and Choose Data for Analysis
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19. Asking Questions and Getting Answers
GIS analysis may involve visualizing data to identify patterns and relationships
sometimes looking at a map isn't enough
find features that match given criteria
Do this by querying the GIS database
Asking questions
Answer is a selected set of features
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20. Two Types of GIS Queries
Attribute
Select features that have one or more attribute values that meet a particular criterion
In a city layer with a population attribute
Select all the cities with population greater than 1 million
Location
Select features whose location meets particular conditions
Usually in relationship to other features
In a cities layer and a major highways layer
Select all the cities that are within 50 kilometers of a major highway
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21. Asking Questions and Getting Answers
Work with features once they are selected
Zoom
A selected set is temporary
Can be saved as a separate layer or exported to a feature class
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22. Finding Features by Attribute
To find features that meet specific attribute criteria
Create a query expression
A logical statement consisting of three parts:
a field name (attribute)
an operator
an attribute value
Can be linked together to include multiple criteria
Compound expressions
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23. Query Expressions Top example Bottom example Simple
Population greater than 50,000
Bottom example
Compound
Two attributes are being queried
Capital cities whose population is greater than 50,000
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24. Finding Features by Attribute
Result of the query
Selected set of the features in the layer
Features are selected on the map
Corresponding records selected in the layer attribute table
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25. Finding Features by Attribute
Cities with a pop >200,000
Selected on the map,
Records are selected in the layer attribute table
Resulting from the query expression POP2000 >
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26. Finding Features by Attribute
Definition query
Query expression is a property of the layer
defines which features from the feature class will be included in the layer
Eliminate features that aren't of interest from the map display
Saves processing time when the layer is queried or used in another GIS operation
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27. Finding Features by Attribute
Cities layer
definition query limits layer features to cities with a pop >200,000
Map is much less cluttered
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28. How do I know the proper format for building an expression?
ArcMap uses a standard computer language called Structured Query Language (SQL) for query expressions.
SQL is also used by ArcMap to access and manage databases
Most of the time you won't need to worry about the details of SQL because you will build your expressions by choosing options in a dialog
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29. Finding Features by Expression
To find features whose location meets a criteria
Use a query expression
A location query is a descriptive statement
Has three parts:
a target ("select from") layer
a type of spatial relationship
a spatially related layer
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30. Finding Features by Expression
Location query statement specifies
Layer to select features from
A type of spatial relationship
Layer you are comparing the first layer to
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31. Finding Features by Expression
Can create location queries based on
Spatial relationships between features in the same layer or in a different layer
Can choose from many different spatial relationships
Four main categories of feature spatial relationships
Distance
Containment
Intersection
Adjacency
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32. Finding Features by Expression
Buildings that are contained by historic preservation features (orange polygons) are selected.
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33. Working with Selected Sets
Examples of what you can do with a selected set of features.
Visually analyze the geographic distribution of the selected features in the map
Summarize or calculate attribute values only for the selected features
Create a buffer around the selected features
Edit the selected features
Generate a report containing attributes of the selected features
Save the selected features as a new map layer that you can display and symbolize independently
Export the selected features to a new feature class to use in other map documents, share with others, or use as input for other GIS operations
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34. Working with Selected Sets
Use a series of queries
To find features that meet a number of criteria
Additive approach
Features are added to the selected set with each query
Subtractive approach
Features are removed from the selected set with each query
Which approach depends on criteria
Approach that reduces processing time
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35. Working with Selected Sets
Can select features by attribute before selecting by location
Interstate 70 selected using an attribute query
A location query found cities within 50 miles of the selected highway
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36. Accessing More Attributes
Not all feature attributes are stored in a layer attribute table
User-defined attributes
Stored in separate, nonspatial tables
Associate a nonspatial table to the layer attribute table
If they share a common field
A field that stores the same data
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37. Accessing More Attributes
The layer attribute table and the economic statistics table both contain a text field that stores two-letter abbreviations for each Canadian province.
The tables can be associated because they have this field in common.
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38. Associating Nonspatial Tables
Two methods
Joins
Relates
Table joins
One-to-one
Each feature has one related record in the other attribute table.
Canadian provinces tables - each province has one unemployment record
Many-to-one relationships
Multiple features may have the same related record
A layer attribute table containing records for several job training offices within each province, related to the same economic statistics table
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39. Associating Nonspatial Tables
When tables are joined
Fields from one table are appended to the other table.
Table joins are virtual
Tables appear connected in ArcMap
But fields from the nonspatial table have not actually been added to the layer attribute table.
Table joins are not permanent
Can remove a table join
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40. What about table relates?
Table relates are designed for
One-to-many
Many-to-many relationships
Based on a common field
It doesn't append the attributes of one table to the other
Can access the related data when necessary
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41. Exercise
Perform a GIS analysis
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42. Examining and Presenting the Results
Graphical and tabular displays can be combined
Include a table in a map layout
Insert a map or graph into a report
How do you decide what to present?
If analysis project produced a lot of new info
Present only the highlights
Spatial information
Best presented in a map
A list of features and their attributes
Better presented in a table or report.
Easily compare attributes to show trends
A graph
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43. Presenting Data in Maps
Maps created while conducting an analysis
Probably not suitable for presenting final analysis results
Prepared quickly
Needs to be visually simple
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44. Presenting Data in Maps
Map used for executing an analysis
Has basic symbology
Only essential layers
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45. Presenting Data in Maps
A presentation map should include info that explains its context and purpose
Add data layers for orientation
such as streets, landmarks, or administrative boundaries
Carefully choose map symbology to
Conform to common convention/industry standards
convey intended message
Label more features
Add callout text or graphics
To draw attention to important features, relationships, or analysis results
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46. Presenting Data in Maps
Map includes
Features and labels to provide geographic context
Detailed symbology
Map focuses on analysis results
Limits sedge species shown to two: those found exclusively within 100 meters of the shoreline
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47. Presenting Data in Reports
Organize, format, and print tabular
Examples of how you can customize a report:
Choose which attribute fields to include
Include all records in a table or a selected set
Sort records based on values in one or more fields
Group records and calculate summary statistics
Sum, average, and count
Choose elements to include
Title, image, or page number
Choose
Tabular format  Fields across the page
Columnar format  fields down the page
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48. Presenting Data in Reports
ArcMap's built-in report generator
Create simple reports to add to a map layout
Alternative to adding a table
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49. Presenting Data in Reports
Report created with ArcMap's report tool
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50. Presenting Data in Reports
To create a report that to use more than once
Save it to a file on disk
Can export reports to different file types
Adobe Portable Document Format (.pdf)
Rich Text Format (.rtf)
Plain text (.txt)
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51. What if I need to create a more detailed report?
When you need to create sophisticated reports, you can use Crystal Reports™.
Access Crystal Reports Wizard from ArcMap Tools menu
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52. Exercise
Map your analysis results
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53. Exercise
Create a report
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54. Review
A GIS analysis involves visualizing and combining geographic data to derive new information.
GIS analysis does not solve problems directly
The information it produces is used by people to draw conclusions and make informed decisions
Key points to remember about GIS analysis.
GIS analysis is an iterative process that includes clearly defining a problem, identifying criteria and data, planning and executing the analysis, and evaluating and presenting the results.
An analysis plan can help you identify necessary data and software tools, prevent mistakes, and save time.
GIS analysis often involves creating queries to select features that meet attribute or locational criteria.
To access feature attributes stored outside the layer attribute table, you can create a join between the attribute table and a nonspatial table.
Maps, graphs, tables, and reports can be used to present analysis results.
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55. Review Questions
What three things should be identified on a workflow diagram?
How can you create a report that lists the attributes of only some of the features in a layer?
Why would you create a table join?
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56. Review Answers
A workflow diagram should identify the sequence of steps, the specific tool to use at each step, and the data required and produced by each tool.
To show the attributes of only some features in a report, first create a selected set of features, then create the report.
You would join two tables if you want to query a layer based on an attribute that is stored outside the layer attribute table.
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57. Key Terms Definition query Join Query Query expression Selected set
A type of attribute query in which the query expression used to select features is a property of the layer and defines which features from the feature class will be included in the layer.
Join
Appending the fields of one table to those of another through an attribute or field common to both tables. A join is usually used to attach more attributes to the attribute table of a geographic layer.
Query
A request that selects features or records from a database. A query is often written as a statement or logical expression.
Query expression
An expression used to select features with particular attribute values. Query expressions are generally formed as an SQL statement and have three parts: an attribute, an operator, and an attribute value. Query expressions can be linked together to include multiple criteria.
Selected set
A subset of features in a layer or records in a table that is chosen by the user.
Workflow diagram
A diagram created to organize and plan a GIS analysis. A workflow diagram should identify the sequence of steps to be performed, the tools to be used, and the data to be input and produced at each step of the analysis.
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