GIS Brownbag Series

Attributes

In the beginning…

Earliest GIS systems did not have attributes

Needed separate layers for labels (e.g. names)

CAD software still maintains different separate layers

Amelia Earhart

Shapefile showing Amelia’s last flight

Right-click on the name of the shapefile for the flight path to open attribute table

LENGTH FROM_CITY TO_CITY

1414.502 Oakland Tucson

2323.930 Tucson New Orleans

1186.745 New Orleans Miami

1783.788 Miami San Juan

974.294 San Juan Caripito

1004.282 Caripito Paramaribo

Attributes:

•Length

•FROM_CITY

•TO_CITY

Feeding sites of a chimp called “Fifi”

Aerial photograph ofGombe National Park.

Feeding sites stored in a shapefile or personal geodatabase

Aerial photograph stored as a raster

Raster attributes

Number of attributes attached to rasters is limited

Shapefile or Personal Geodatabase Attributes

Many attributes can be attached to each feature

OBJECTID and Shape attributes are automatically

generated by ArcGIS

Attributes can be:

• Numbers (whole or with decimal places)

• Names or text

• Dates

• Hyperlinks

Depending on type of attribute different maps can be created

This map was created based on text attribute

Numbers allow to display population size

Depending on type of attribute different analysis can be done

What if you want to show the area for

each County?

Adding fields to an attribute table

Step 1: Create a new attribute that will hold the area

B. Click “Options” button. Then select “Add

Field”

A. Open attribute table

If “Add Field..” is “greyed-out” stop edit session and try again

Pick any name you like. Must be < 11 characters

Other choices: Text, Date, Short or Long Integer

Number of spaces to store a number

Number of decimals. E.g. 1.1234

The new attribute “Area” has been added!

Right-click on “AREA” and select

Calculate Geometry

Notice how all the area’s are set to “0”

Step 2: Calculate the area

Joining other data to attribute tables

Table with population size for each County

Goal: show those numbers on a map

Solution: join this data to the shapefile from previous slide

Step 1: Save your data in Excel as a DBF4 file

Add your .dbf file to ArcMap

Determine how you are going to join your data

Join “population” table to shapefile

Look for a primary key: an attribute that both tables have in common and that can be used for the join.

Here: both tables have County names

Joining tables

Right-click on the shapefile

Choose “No”

Make sure that primary key is the same data type in both tables:

E.g. you can not join numbers to text.

Data from shapefile

Data from “population” table we joined to the

shapefile

Tip: export joined table to new shapefile

Map showing population size for each County

Maybe population density would be a more informative map..

Density is “POPULATION” / “AREA”

Add a new field to store density attribute

Right-click on

DENSITY

Types of Relationships

This is a one-to-one relationship

One record in the shapefile matches one record in the population table

FID Name

0 Joe

1 Kelly

2 Dan

3 George

4 Spencer

5 Mike

Name Pet

Joe Cat

Joe Dog

Kelly Cat

Dan Dog

Mike Snake

Mike Cat

Mike Hamster

Is this a one-to-one relationship?

?

Types of Relationships

Can we join this data?

NO! Instead of “join”, use a “relate”

NO! It is a one-to-many

Relates: Example

DBF table with information about a few

different laterals

Goal: we want to look at those laterals on a map

This is the NHD: it has the geometry

Relate NHD to the laterals table

This is a one-to-many relationship

H Canal is selected

Use “info” tool on this line segment

Attributes for that line segment

By clicking the + you see related

tables

Tables that NHDFlowline layer is

related to

By relating tables the user has much more

information at “his/her fingertips”

Upcoming Brownbag Lectures

May 20: Model Builder

June 17: How to make maps that communicate

Check out previous Brownbag Presentations on WEnet