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Attribute Tables

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Data table format

•Rectangular table with one value per cell-Columns (fields) are attributes -Rows are observations (data)

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Data table format

•First row must have column names that are self-documenting labels-e.g., Pop5To17, Area-First character is a letter-Remaining characters can be any letter, digit, or the underscore character (but no blanks)

•All additional rows of a data table must contain only attribute values-None of the rows can be sums, averages, or other statistics for other rows

•Sometimes columns can be functions of other columns (sums, averages, etc.)

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Primary keys

Each data table has a primary key with two properties-Each value in the attribute column is unique-There are no null values

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FIPS Geocodes

•Federal Information Processing Standards-Developed by the National Institute of Standards and Technology-Codes for place names throughout the world

– countries– states/provinces– counties– metropolitan statistical areas (MSA’s)– cities– places - Indian reservations, airports, and post offices in the

US

See http://www.genesys-sampling.com/pages/Template2/site2/61/default.aspx for additional geocodes.

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FIPS Geo codes: Hierarchy

Country: US

FIPS codes

County: 003 (Allegheny)

State: 42 (Pennsylvania)

Tract: 0501

Block: 12 (US420030501312)

Block Group: 3Census codes

Minor Civil Division: 85188 (Wilkinsburg)

Parcel (Block & Lot#)Local government cadastral data

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ANSI Codes

American National Standards Institute (ANSI)

Codes

www.census.gov/geo/www/ansi/ansi.html

Replaces FIPS codes

In many cases, the codes are the same (e.g. Pennsylvania, Allegheny County =

42003)

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External table file formats for import to ArcGIS

•Plain ASCII text with comma separated values (.csv)-Very transportable format, very large files-Each table record is a row terminated with a line-break character-Has values separated by a delimiter, usually a comma-For data values that contain the delimiter, enclose the value in double quotes-Sometimes columns get wrong data type on import (use double quotes to force text data type for digits, say for house numbers)

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External table file formats for import to ArcGIS

•Excel (.xls, .xlsx)-Excel 2003, up to 65,000 rows and 256 columns-Excel 2007, up to 1,048,576 rows and 16,384 columns

•dBase database table(.dbf)-Legacy format-ArcMap truncates field names to 1st 10 characters-dBase IV has max of 255 columns-Can open dBase file in Excel but cannot save Dbase from Excel

•Microsoft Access database (.mdb)-Up to 2GB file size-See following for other limits: http://www.databasedev.co.uk/access_specifications.html

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Field calculator (numeric)

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Field calculator (numeric) Calculate acres to square miles

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Field calculator (text)

Concatenate house number and street fields

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Field calculator (text) Populate field with county name

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Data Table Joins

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Joins

•Feature attribute tables, data tables•Puts two tables together, on the fly, to make one table-One-to-one join-One-to-many join

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Example join

=

U.S. Counties GIS layer

Unemployment databases +

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Determine Fields to Join

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Create New Field

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Columns Ready to Join

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Join Data• Right-click Counties layer > Joins and Relates > Join

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Resultant Attribute Table

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Classifying Unemployment

•Values will only appear with number fields

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Final MapPercentage Unemployment by U.S. Counties, 2005

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Problems with Joins

• Field types are different (e.g. one is numeric and one is text)

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Problems with Joins

• Data is different

Must remove dashes!

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Problems with Joins

• Too much formatting in Excel• Keep it simple!

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Spatial Joins

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Spatial Joins

•Joins using shape (not attribute field)•Enables data aggregation (counting or summing points by polygon)

•Common Spatial Joins-Points to Polygons (counts)-Polygons to Points (adds text)-Points to points (distances)

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Points to polygons

How many convenience stores are in each neighborhood?

•Start with:-Store points-Neighborhoodpolygons

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Points to polygons

• Right-click neighborhoods > Joins and Relates > Join

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Spatial join result

New polygon layer with count of points (number of stores)

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Spatial join result

Show as a choropleth map, with labels, or tableNeighborhood Store CountBloomfield 22Central Business District 12Strip District 10Brookline 10Central Lawrenceville 8Larimer 8Middle Hill 7Central Oakland 7Squirrel Hill South 7South Oakland 7Carrick 7Highland Park 6Garfield 6North Oakland 6Terrace Village 6Brighton Heights 5Shadyside 5Morningside 4Marshall-Shadeland 4East Liberty 4Friendship 4Sheraden 4Homewood South 4Greenfield 4

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Polygons to points

What neighborhood is a store in?

•Start with:-Store points-Neighborhoodpolygons

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Polygons to points

•Right-click business points> Joins and Relates > Join

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Spatial join result

Point shapefile with neighborhood data on each store

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Points to points

How close is a school to a store?

•Start with:-Store points-School points

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Points to points

Right-click school points> Joins and Relates > Join

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Result Join

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Geodatabases

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Geodatabases

A geodatabase is a container used to hold a collection of datasets (GIS features, tables, raster images, and other objects).

Country layer

Graticule layer

World.gdb

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Geodatabase types

File geodatabase (.gdb) •stores datasets in a folder of files

•each dataset a file up to 1 TB in size

•can be used across platforms

•can be compressed and encrypted for read-only, secure use

•ESRI’s recommended choice

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Geodatabase types

Personal geodatabase (.mdb)•stores datasets in a Microsoft Access format

•storage sizes between 250 and 500 MB

• limited to 2GB

•only supported on Windows

ArcSDE geodatabase•stores datasets in a number of optional DBMSs:-IBM DB2, IBM Informix , Microsoft SQL Server , Oracle, or PostgreSQL

•unlimited size and users

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New file geodatabase

ArcCatalog

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Import into geodatabase

Shapefile features

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Import into geodatabase

Tables

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Export from geodatabase

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View geodatabases Cannot identify names in Windows Explorer

Must use ArcCatalog

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Compact geodatabases

File and personal geodatabases•Reduces size and improves performance

•Compact personal geodatabases > 250 MB.

•Geodatabases with frequent data entry, deletion, or general editing

•Open geodatabases in ArcMap cannot be compacted-remove any layers with a source table or feature class in that database from the TOC

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Compress geodatabases

File geodatabases•Once compressed, a feature class or table is read-only and cannot be edited

•Compression is ideally suited to mature datasets that do not require further editing

•Compressed dataset can be uncompressed to return it to its original, read-write format

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ArcCatalog

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ArcCatalog utility program

Like Windows Explorer but for Esri-format data•Copy, delete, rename, move, search files, view metadata•Import/export popular spatial data format files•Create new shapefiles, file geodatabases, etc. for input in ArcMap

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Basic functions Copy, paste, rename, etc.

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View and edit properties Projections, fields, etc.

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View metadata

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Edit metadata

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Create new files Geodatabases, tables, features, etc.

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Calculating Geometry

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Point Centroids

Used to display and calculate data

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Point centroids

When displaying or analyzing small polygons it is often better to use point centroids

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Calculate XY fields

Add new X and Y fields in the attribute table

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Calculate XY fields

Calculate geometry for X field, repeat for Y

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XY field results

Results are X and Y values based on map properties (e.g. Long/Lat or XY feet)

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Export XY coordinates

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Add XY data table

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Export as shapefile

XY events should be exported as permanent shapefile or feature class

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Counting Point Centroids

Population spatially joined to buffer around toxic release sites

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Calculate area

Add area field and calculate geometry

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Calculate perimeter

Add perimeter field and calculate script

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Calculate length

Add length field and calculate script