Geodatabases Outline Data types Geodatabases Data table joins Spatial joins Field calculator Calculate geometry ArcCatalog functions
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Directly loadable data types
dBase (.dbf) Text with comma (.csv) or tab-
separated values (.txt)
Microsoft Access (.mdb)
Microsoft Excel (.xls)
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Data table formats First row must have attribute names
with self-documenting labels (e.g. Pop5To17, Area)
Usual naming convention first character is a letter remaining characters be any letters, digits,
or the underscore character All additional rows of a data table
contain attribute values None of the rows can be sums,
averages, or other statistics of raw data rows
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Geodatabase typesManages features and tables inside a database management system
File geodatabase stores datasets in a folder of files each dataset file up to 1 TB in size can be used across platforms can be compressed and encrypted for
read-only, secure use
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Geodatabase types Personal geodatabase
stores datasets in a Microsoft Access .mdb file
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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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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Data table joins Putting two tables together to make
one table
Join two tables one-to-one by row
Must have the same values and data
types
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Join example
Housing heating fuel study for U.S.
Counties
Source: U.S. Census Data table: Census SF3 table for heating
fuel by county
Map Features: County polygons
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Data table
Heating fuel table data dictionary H040001: Occupied housing units: House heating fuel; TOTAL Units H040002: Occupied housing units: House heating fuel; Utility gas H040003: Occupied housing units: House heating fuel; Bottled; tank;
or LP gas H040004: Occupied housing units: House heating fuel; Electricity
H040005: Occupied housing units: House heating fuel; Fuel oil; kerosene; etc.
H040006: Occupied housing units: House heating fuel; Coal or coke H040007: Occupied housing units: House heating fuel; Wood H040008: Occupied housing units: House heating fuel; Solar energy H040009: Occupied housing units: House heating fuel; Other fuel H040010: Occupied housing units: House heating fuel; No fuel used
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Data problem FIPS has leading zero
and is a TEXT field.
GEO_ID2 is a NUMBER fieldwith no leading zeros.
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FIPS
01001
01003
01005
01007
GEO_ID2
1001
1003
1005
1007
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Data solution Make a new NUMBER field in Counties
attribute table and use field calculator to populate new field from old
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Data solution New FIPS_NUM is same as GEO_ID2 and
ready to join
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Join result Heating fuel data is now listed for
every county in the USCounties feature attribute table
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Permanent joins Joins are temporary and can be
removed Export data to make joins permanent
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Spatial join example You have census block group centroids
with housing fuel data
You want to know housing fuel data by neighborhoods
No attributes in common Spatial join needed
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Spatial joins Points to polygons
Spatially joins points (block centroids) within polygons (neighborhoods)
Joins using “shape” (not attribute field)
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Sum result Every block group centroid has associated
data (e.g. H040004, heating electricity shown in
labels)
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Sum result
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One neighborhood example Central business district
4 block groups Housing units with electricity fuel (80 + 299 + 128
+ 292 ) Sum = 799
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Other spatial joins
Polygons to points Example: ATM robberies (points) need
neighborhood name
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Polygon to point join result
Neighborhood name shows on each
point
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Other spatial joins Points to points
Example: What is the distance of a burglary to the nearest commercial property?
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Point to point join result Distance to nearest commercial
property shows on each burglary point
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FIELD CALCULATORLecture 4
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(as in “Feature-Attribute” Calculator)
Sample functions
Performs numeric calculations
Populates field
Concatenates text data
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Field calculator functions
Calculate acres to square miles
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Field calculator functions
Populate field with county name
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Field calculator functions Concatenate house number and street
fields
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Polygon/point centroids Advanced calculations for finding a
polygon’s point centroid
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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 as shapefile XY events should be exported as
permanent shapefile or feature class
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