1. GIS Lecture: Data

2. Outline
Data Types, Tables, and Formats
US Census Files
Tabular Joins

3. Data Types, Tables, Formats

4. Directly Loadable Data Types
dBase (.dbf)
- field name maximum length of 10 characters
Text with comma- or tab-separated values (.csv)
Microsoft Access (.mdb)
Excel (.xls)

5. Proper Data Table Formats
First row must be the field names
(e.g., Pop5To17, Area, and Capacity)
Field naming convention
first character is a letter
others can be letters, digits, or the underscore character (no spaces)
All other rows contain attribute values

6. US Census Files

7. Example census geographies

8. Decennial census data Every 10 years: Population Age Sex Race Families
Households
Housing units

9. American Community Survey (ACS)
Randomly selects about 3 million addresses each year to participate
Has rolling, 1-, 3-, and 5-year estimates and 90% confidence intervals

10. ACS Data Age Sex Race Family and relationships Income and benefits
Health insurance
Education
Veteran status
Disabilities
Where you work and how you get there
Where you live and how much you pay for certain essentials

11. ACS estimates 1-year 3-year 5-year Most current
Data with populations 65,000+
Smallest sample size
Less reliable
3-year
Data with populations 20,000+
Larger sample size than 1-year
More reliable than 1-year but less reliable than 5-year
5-year
Data for all areas (tracts and block groups)
Largest sample size
Most reliable but least current

12. U.S. Census Data Tables http://factfinder2.census.gov
SF-1 vs ACS (American Community Survey)

13. File clean-up in Excel Import into Excel Text vs. Numeric data
Combine fields
Rename the file and save

14. Tabular Joins

15. Tabular Joins Putting two tables together to make one table
Join with common field attributes
Common fields do not need to have the same field names
Must have the matching values and data type (e.g., text vs. numeric)

16. Tabular Join Example Map parcels according to their value
Data Table – parcel values
Parcels Shapefile

17. Property Value Data Has no geography
Does have fields for Parcel ID and LandValue

18. GIS Parcels Layer

19. Choose Fields to Join

20. Join Data

21. Join Result
Property fields are added to the Parcels attribute table

22. Map with Property Data

23. Problems with Joins Data in fields not exactly the same
Must remove dashes! 23

24. Problems with Joins
Different data field types
text
numeric

25. Summary
Data Types, Tables, and Formats
Geodatabase
Tabular Joins