QGIS Module 2

SessionTwo:

•Attribute Tables and

•JOIN: how to add data to QGIS

Why are attribute tables

important?

Attribute tables define the elements of a

shapefile and allow you to see what is

“inside” the layer. They also allow you to

zoom, highlight and select for other

operations.

“Flat File” with columns and rows

Row = geographic feature record

Column = attribute field (item of

information about a feature)

Attribute field general types

• Numeric (integer or decimals)

• Text (string)

• Date

• Blob (binary large object)

Source: http://www.esi.utexas.edu/gk12/workshops/gis/ppts.php

Each different layer has its own attribute table so when we open a new one here…

ATTRIBUTE TABLE CAN BE USED TO ZOOM INTO A SELECTED FEATURE – IN THIS CASE A DISTRICT; HIGHLIGHT THE ENTIRE ROW TO SELECT IT

THE SELECTED FEATURE IS LARGE AND HIGHLIGHTED IN YELLOW

YOU CAN USE THE ZOOM FEATURES ON THE TOOLBAR TO ZOOMOUT TO SEE THE SELECTION IN CONTEXT OF THE COUNTRY

De-select on toolbar to end

the highlighted area

JOIN

• Basic to all GIS programs is “joining”

• This is how tables of data (excel, csv,

etc) are transformed into maps

• For example, HIV prevalence by

province

Change data form

Must change the data format from EXCEL

or other database into a form that QGIS

can use

• The easiest process is using .dbf

• .dbf is an “old” data file type (dbase)

BUT shapefiles contain .dbf file data

which is why we use them

• To convert we need LibreOffice

LIBRE OFFICE

• Open Libre office and open your excel

data (name of excel file or type of data)

In Libre Office choose spreadsheet

View the data you want to add.. Save as “name”.dbf inside data folder

Open or maximize QGIS

• You will now add your .dbf file that you

created in Libre Office to the map layers

you are already displaying

• Click on “add vector layer”

1.

2.

3.

Open “attribute layer” for

moz_adm1

• Find the column that has the name of

the provinces in it.

JOIN in QGIS

• Double click on moz_adm1

• When layer opens click on “join” tab

11.You will see this. Note

default target field ID_0

2. You MUST change target

field!

You need to match “like” with “like” so if you have province

data, in this case provincia, you must match with QGIS’s

province layer, in this case NAME_1.

Return to Map Layers and

double click on moz_adm1

Check to see that the

two layers have been

added by hitting the

tab called fields.can

you see them?

DOUBLE CLICK

ON MOZ-ADM1

CLICK ON

GENERAL, NOW

CHANGE THE

TITLE TO RESAVE

THE LAYER

UNDER A NAME

WHICH REFLECTS

YOUR DATA

RENAME

THE FILE

CLICK OK

“Joining”: putting table data

inside the map layer

Now make

sure to

change the

column so it

is set to the

file with

prevalence

that you

wish to

map. You

DO NOT

want

Column set

to ID_0

which is the

default. It

will crash

your

computer.

How to change the

classification

Double click on a row to begin. Be sure to select “label” afterward to ensure that your changes are reflected in your labels. This is also an opportunity to simplify the label presentation.

Prevalence map with province

names

OK! Now try this with your

own data….

If you don’t have data make

up data to practice

Adding two variables to one

map layer

How to map a second

presentation of prevalence

onto one map: using symbols

• This step shows you how to map a

second level of prevalence, HIV

prevalence in men (MHIVPREV) onto a

map where the colors of provinces

represent the HIV prevalence of women

Here is the final map

with the male and

female HIV prevalence

Male HIV

prevalence is

represented as

the pink dots and

female HIV

prevalence is

represented

within the blue

shaded province

layers.

Now go back to the diagram

layer, where you see pie chart

and choose text diagram.

What do you think?

End session 2

Thank you!