GIS Lecture: Data

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

Data Types, Tables, Formats

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)

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

US Census Files

Example census geographies

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

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

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

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

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

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

Tabular Joins

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)

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

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

GIS Parcels Layer

Choose Fields to Join

Join Data

Join Result Property fields are added to the Parcels attribute table

Map with Property Data

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

Problems with Joins Different data field types text numeric

Summary Data Types, Tables, and Formats Geodatabase Tabular Joins