return to outline copyright © 2009 by maribeth h. price 4-1 chapter 4 attribute data
TRANSCRIPT
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Chapter 4
Attribute Data
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Outline• GIS Concepts
– What is a table?– Queries on tables– Joining and relating tables– Summary statistics– Database storage concepts
• About ArcGIS– Working with tables in ArcGIS– Editing and calculating fields – Using Excel data with ArcGIS
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What is a table?
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Table terminology
TitleField
Records
Each field is specifically defined and established before any data can be
entered.
Field definitions control the type of data that can
be stored in a field.
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Types of tables
• Attribute table– Stores attributes of
map features– Associated with a
spatial data layer– Has special fields for
spatial information
• Standalone table– Stores any tabular data– Not associated with
spatial data– OID instead of FID
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Database Management Systems
• Dedicated systems for managing tables of data
• Provide data management for agencies, universities, companies, etc.
• Designed for multi-user environments with enhanced security needs
• Focus on data tables with tools for queries, reporting, graphing, etc.
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Queries on tables
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What is a query?
• A query extracts certain records from a table based on a specified condition– How many students have GPA > 3.5?– How many states have population > 1 million?– How many counties had greater population in
1990 than in 2000?– How many customers have last names
beginning with “Mac” or “Mc”?
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SQL
• Many databases use a special query language called Structured Query Language
• Can write queries that work in multiple DBMS environments
• Queries can be saved and reused
• Nearly always case-sensitive
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SQL Query ExamplesSome Valid Queries
SELECT *FROM cities WHERE "POP1990" >= 500000
SELECT *FROM counties WHERE “BEEFCOW_92” < “BEEFCOW_87”
SELECT *FROM parcels WHERE “LU-CODE” = 42 AND “VALUE” > 50000
SELECT *FROM rentals WHERE “RENT” > 700 AND “RENT” < 1500
Programs may have an interface to help users build SQL expressions In most databases, SQL
expressions are case-sensitive “Smith” ≠ “SMITH”
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Searching for partial matches
• Sometimes you need to find one string within another rather than an exact match– Find all customer names beginning with
“Mac” or “Mc”– Find all zip codes beginning with 0
• Typically uses a “wildcard” character– *Mac* or *Mc*– 0*
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The Like Operator
• “NAME” LIKE ‘%(D)%’ – Finds all of the (D)
Democrats
• % is wildcard• Ignores Don or Danforth
• “NAME” LIKE ‘%New %’ – Would find New Hampshire
and New York, but not Newcastle or Kennewick
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Query results
• The result of a query is a set of selected records that meet the criteria
• Subsequent operations on the table will use only the selected records and ignore the others. A user might…– Export the selected records to a new table– Calculate statistics on the selected records– Calculate new values for the selected records– Produce a report based on the selected
records
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Joining and relating tables
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Joining tables
Join tables on common field
Joined table
Destination table Source table
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Join facts
• Joins are temporary relationships between tables used by a relational DBMS
• Tables must share a common field (key)
• Treats the two tables as a single table
• Original stored data is not affected
• Can be removed when no longer needed
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One-to-one joins
When each record in the destination table matches exactly one record in the source table, we call it a cardinality of one-to-one.
Destination table (always imagine on the left)
Source table(always imagine on the right)
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Types of Cardinality
• One-to-one– States to Governors– Husbands to wives
• One-to-many– States to cities– Districts to schools
• Many to one– Cities to states– Schools to districts
• Many-to-many– Students to classes– Stores to customers
In evaluating cardinality, always put the destination first.
(Destination on the left)
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Rule of JoiningEach record in the destination table must match one and only one record in the source table.
One to one
Destination table Source table
Many to one
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One to many
Destination table Source table
?
Violates the Rule of Joining
Record to join to destination is ambiguous
Must use a relate instead
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Relates
• Similar to a join except that– The tables remain separate– Items selected in one table may be
highlighted in the related table
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States: Select the New England States
Congress Reps of New England States
Related tables
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Summary statistics
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Statistics on a table field
Based on values in a field. Includes all records or a subset based on a query.
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Summarizing tables
• Calculate statistics for groups of features in a table• Groups by unique values in the one field• User chooses statistics to calculate for other fields• Produces another table as output with groups and stats
How many people live in each subregion?
What is the total area of each subregion?
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Summarizing tables
How many earthquakes in each state?
Total deaths and damage in each state?
Average magnitude in each state?
Historic major earthquakes
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How to summarize
Right-click State field
Sum Deaths
Sum Damage
Average Mag
Average MMI
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Database storage concepts
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Fields
• Fields have specific types available
• Must be defined before use
• Once defined, cannot be changed
• Naming rules– No more than 13 characters– Use only letters and numbers– Must start with a letter
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Binary data
• Fundamental mode of computer storage• Data are stored as a series of 0’s and 1’s
representing numbers in base 2 (bits)• Bits are grouped by eight to form 1 byte. A
megabyte (MB) is 1 million bytes.
10011101
1 bit
one byte
In base 2:00000000 = 0 11111111 = 255
28 = 256
1111111111111111 = 65,565216 = 65,566
two bytes
01
1011
100101110111
1000100110101011
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ASCII storage
• American Standard Code for Information Interchange (ASCII)
• Stores letters, characters, and symbols as single 7-bit binary codes
CAT = {67,65,84} decimal = 100001110000011010100
cat = {99,97,116} decimal = 110001111000011110100
148 = {49,52,56} decimal = 011000101101000111000
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About ArcGIS
Chapter 4.
Attribute Data
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Working with tables in ArcGIS
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Tables in ArcGIS
• Tables contain attribute data
• Many formats, one interface
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Sources of tables
• Dbase files
• INFO files
• ASCII Text files (tab or comma delimited)
• Records from SQL database systems
• Excel worksheets
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ArcMap table interface
TitleField Right-click field
name to get menu
Records
Status bar Options menu
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Adjusting field width
• Temporary, does not affect stored file
Hover over field break to get double arrow, then drag
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Field properties tab
Field alias
Hide field
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Shortcut to field properties
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Formatting field display
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Table appearance
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Sorting tables
• Has no effect on original data
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Select by Attributes
• Some valid queries
[POP1990] > 1000000
“STATE_NAME” = ‘Alabama’
[POP2000] >= [POP1990]
Note:
DBF tables have field names enclosed in quotes
Geodatabase tables have field names enclosed in brackets
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Selecting records
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Show selected
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Clear SelectionOn toolbar
From table options menu From main menu
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Field statistics
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Statistics
• Statistics for fields are based on the selected records
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ArcGIS field data types
Geodatabases and shapefiles
Short Integers stored as signed 2-byte binary numbers(value range from -32,000 to +32,000)
2551201
Long Integers stored as signed 4-byte binary numbers(value range from -2 billion to +2 billion)
156000
FloatFloating point values with 8 significant digits in
the mantissa1.2893851e12
DoubleDouble-precision floating point values with 16
significant digits in the mantissa1.111111111111
111e13
Text Alphanumeric strings ‘Maple St’
Date Date format 07/12/92
BLOBBinary large object; any complex binary data
including images, documents, etc.
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Field characteristics
• Length– The total characters a
text field can store
• Precision– The total width of
digits a numeric field can store
• Scale– The number of
decimal places
Length = 10Maple St.Maple Stre
1561985.128-1922.5600
0.0010.00001
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Adding a new field
• In ArcCatalog layer properties
43
1
5
2
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Adding a field• In ArcMap
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Editing and calculating fields
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Editing fieldsOpen Editor toolbar Start editing
Type edits in fields Save edits, stop editing
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Calculating fields
Add a new field if necessaryConsider whether you need decimal places!
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Calculate
Right-click field to calculate
Enter expression
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Geodatabase geometry measures
• Automatically created and maintained– Usually appear at end of table
• Shape_Area field• Shape_Length field
– Units will match units of the coordinate system
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Coverage geometry measures
– Automatically constructed– Updated whenever the BUILD or CLEAN
command is used to update topology• LENGTH field in arc tables• AREA field in polygon tables• PERIMETER field in polygon tables
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Shapefile geometry measures
• Shapefiles DO NOT create or maintain these fields automatically!– Must be created and updated manually– Some functions and operations can change
the lengths and areas of features– If you find an AREA field there is no
guarantee that it is correct
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Be careful!
Before After
AREA/LENGTH/PERIMETER fields in shapefiles are NOT automatically updated if features change.
Don’t use one of these fields unless you are CERTAIN that they are correct.
These area/perimeter fields are likely from a coverage
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User geometry calculationsCreate field to hold values
Choose type, coordinate system, and units
Not automatically updated if features change!!!
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Test yourself: True or False?
• A field named AREA in a shapefile will always have the correct area?– False. Shapefile area fields are not automatically
maintained.
• A field named AREA in a geodatabase will always have the correct area?– False. Automatically updated fields in a geodatabase
are called Shape_Area.
• A field named AREA in a coverage will always have the correct area?– True. Automatically updated area fields in a
coverage ARE called AREA.
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How to join or relate tables
To start, right-click the
destination table.
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Using Excel data with ArcGIS
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Excel files
• Excel worksheets with suitable layout can be opened as tables in ArcGIS
• Most functions that do not involve changing the file will work (sort, query)
• Tables cannot be changed or edited
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Excel file requirements
• First row must contain field headings with legal field names as defined earlier
• No blank rows or formulas should be used• Each column should contain only text or
only numbers.• It is helpful for each column to be
formatted as text, numeric, etc.• ArcMap cannot open files that are already
open in Excel—they must be closed first
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Acceptable WorksheetCorrect field names
Columns formatted as text or numeric
No formulas or blank lines
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Workbooks and worksheets
• An Excel workbook file (.xls) may contain more than one worksheet.
• By default there are three named Sheet1, Sheet2, Sheet3.
• There may be one or more named worksheets.
• ArcMap can only open one worksheet at a time.
• You will open the workbook like a folder and select a single worksheet
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Adding a worksheet
1. Add data button2. Open workbook file like a folder
3. Add named worksheet, or the first unnamed worksheet.
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Excel file in ArcMap
You can use x-y locations in a table to produce points on a map.
But first you must know the coordinate system of these
locations. What is this one?
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Add XY Data
You MUST use the Edit button to define the coordinate system.
Degrees indicate a geographic coordinate system (GCS). NAD83 is the most common in use today, but if you know it is something different you must use that.
Other tables might have units in UTM meters, State Plane feet, etc. You must know the coordinate system to create usable, correctly located points.
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Oregon climate stations
• Stations appear as points on the map, an “event layer”
• Export to shapefile or feature class to keep permanently