This document provides instructions for using attribute tables and joining data in QGIS. It discusses how attribute tables define the elements of a shapefile and allow users to view, select, and highlight geographic features. It then explains how to join external data stored in files like Excel and CSVs to shapefile layers in QGIS by converting the external files to DBF format and linking fields between the files and layers. The document demonstrates this process to map HIV prevalence data from a DBF file to administrative boundary layers in Mozambique.

1. SessionTwo:
•Attribute Tables and
•JOIN: how to add data to QGIS

2. 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.

3. “Flat File” with columns and rows
Row = geographic feature record
Column = attribute field (item of
information about a feature)

4. 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

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

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

8. THE SELECTED
FEATURE IS LARGE AND
HIGHLIGHTED IN
YELLOW

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

10. De-select on toolbar to end
the highlighted area

11. 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

12. 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

13. LIBRE OFFICE
• Open Libre office and open your excel
data (name of excel file or type of data)

14. In Libre Office choose spreadsheet

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

16. 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”

18. 1.
2.
3.

19. Open “attribute layer” for
moz_adm1
• Find the column that has the name of
the provinces in it.

22. JOIN in QGIS
• Double click on moz_adm1
• When layer opens click on “join” tab

24. 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.

25. Return to Map Layers and
double click on moz_adm1

26. Check to see that the
two layers have been
added by hitting the
tab called fields.can
you see them?

27. DOUBLE CLICK
ON MOZ-ADM1
CLICK ON
GENERAL, NOW
CHANGE THE
TITLE TO RESAVE
THE LAYER
UNDER A NAME
WHICH REFLECTS
YOUR DATA

28. RENAME
THE FILE
CLICK OK

31. “Joining”: putting table data
inside the map layer

34. 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.

36. 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.

40. Prevalence map with province
names

41. OK! Now try this with your
own data….
If you don’t have data make
up data to practice

42. Adding two variables to one
map layer

43. 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

45. 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.

46. Now go back to the diagram
layer, where you see pie chart
and choose text diagram.
What do you think?

47. End session 2
Thank you!