Skill Development Lab 2

Description

In Module 2, you learned about the difference between thematic and reference maps. In your first skill development lab, you made a rough reference map, specifically a political map, showing country and state boundaries. In this module we will focus on the different types of thematic maps you learned about in Module 2 and how to make them in QGIS. Additionally, in this module, you learned about the importance of matching the visual hierarchy to the intellectual hierarchy and will have the opportunity to put that into practice in this lab. As you implement the skills you learned about in Module 2, we will also be answering a geographic question, specifically: How is population geographically distributed across the United States? In this lab, you’ll create a series of thematic maps (a dot density map, a choropleth map, and a proportional symbol map) answering that question. As you do, think about the underlying structure of each type of map and consider how the type of map affects the argument that the map can make. This lab should take approximately 2-2.5 hours to complete. This lab is worth 40 points.Submit two mixed symbols map made using QGIS. (Required – 40 points) OBJECTIVESChoose symbolization strategies that align with the argument the map is makingMatch the visual hierarchies on the map with the intellectual hierarchies of the map’s argument.

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GEOG 360: GIS & Mapping
Instructions:
1. Set up the lab.
a. Download the Lab 2 Data folder from Canvas. Remember to unzip it and then
save it to a designated folder for your class GIS work. Because maps in QGIS link
to your data rather than importing the data into your map document, once you
have your data and map saved on your computer, you don’t want to move them
around in relation to one another. As such, I highly recommend you save them
into a designated folder and then not move stuff around within that folder.
b. In the first skill development lab, you learned how to access QGIS on your
personal computer. Go ahead and open it up. If you need to refer back to Lab 1,
feel free.
c. Remember to start by saving your file (ideally to the folder you dedicated to your
GIS work for this class).
d. Take a few minutes to remind yourself where your mapping window, Browser
panel, Layers panel, toolbars, and cursor tools (zoom in, zoom out, and pan map
(the hand that allows you to click and drag your map around)) are. Refer back to
your first skill development lab if you need a refresher.
2. Now, let’s add our data.
a. Remember that we can navigate to our data using the Browser panel. You can
then add a shapefile to your map by double clicking on it or clicking and dragging
it into your Layers panel. For this lab, you should see two shapefiles (Counties
and States)—please add both.
3. Let’s start by examining our data
a. Shapefiles typically contain attribute data within them (or can be joined to tables
with attribute data). We will start with the States shapefile. To view the
attribute data that is in that shapefile, right click on the States shapefile in the
Layers panel and select ‘Open Attribute Data.’
b. You should see an attribute table open in another window. Notice that we have
7 columns. One contains the name of the state. Another the sequence in which
the state is drawn on your map. Then we have two codes—the GeoID and the
State FIPS code. Both are census codes for each state—the GeoID column shows
what is called a long-form unique identifiers for each US state. They start with a
country code (0400000US) which is the same for each since these are all US
GEOG 360: GIS & Mapping
states. They then have the state FIPS code (ranging from 01 to 56) which are
unique to each state. You’ll notice that the short-form unique identifier (labeled
STATE_FIPS) matches the last two digits of the long-form unique identifier
(labeled GeoID). We will talk more about unique identifiers in a couple weeks,
but for now, just notice that they are there. Finally, we also have columns listing
the region each state falls in, the state abbreviation, and the population of each
state.
c. Since we are going to be answering a question about the geographic distribution
of population in the US, we will be using the “Population” column, so make note
of the column title and then close the attribute table window and return to your
main mapping window.
4. Make a choropleth map
a. Now, we get to make our first thematic map. To do so, right click on your States
layer in your Layers panel and select Properties.
b. You should see a pop-up window with a list of tabs along the left-hand side.
Since making a choropleth map is about symbolizing our data, we are going to
use the Symbology tab (third tab down with a picture of a paintbrush).
c. Once you click on the Symbology tab, you’ll see at the very top that there is a
drop-down menu that will say “Single Symbol.” This just means that at the
moment, all of your states are represented with a single symbol. This is the
default until we change it. Go ahead and click on the drop-down menu and
change it to “Graduated.”
d. Underneath where it now says “Graduated” you’ll see a section asking what
“Value” you want to vary (or graduate) the color based on. Here, you’ll want to
use the drop-down menu to select that “Population” column that we identified
in step 3c above.
e. Now, we can also change our color ramp. The default is to go from white to red,
but you can play around with it to find a color you like. You can use the dropdown menu to select an existing color ramp or you can click on the color ramp
itself to have more options. Pick or make a color ramp that you think does a
good job of showcasing the relative differences in population between states.
f. Once you have set a color ramp that you like, click on the “Classify” button about
two thirds of the way down the Symbology window. We will explore the idea of
classification more in the next lab. Once you hit the “Classify” button, you
should see some categories with their accompanying colors from your color
ramp appear in your main symbols window in the center of the Symbology
GEOG 360: GIS & Mapping
window. When you do click “OK” in the lower right-hand corner of the window
to return to your map.
TIP: If your map disappears when you click “OK,” try clicking the “Zoom Full”
button (a magnifying glass with three arrows pointing out from it) in your
toolbar.
5. Repeat all of the parts of step 4 with the counties shapefile to make a second
choropleth map of population at the county level.
6. Now that you have made two choropleth maps, let’s try a proportional symbol map.
a. Remember that when making proportional symbol maps from areal data (that is
data that represents polygons, in this case states), we typically use a circle placed
at the center of the unit and adjust the size of the circle according to the data
variable.
b. We will start by making a dataset showing those circles. Circles placed at the
center of an areal unit are called centroids. To make a dataset of centroids in
QGIS, click “Vector” in the menu at the very top of your screen, then select
“Geometry Tools” and then “Centroids…”. This should open a Centroids pop-up
window.
c. As your “Input layer” select the States shapefile from the dropdown menu. Then
under Centroids where it says “[Create temporary layer]” click on the “…” button
and select “Save to File.” Select “SHP files (*.shp) as the file type, give it a name,
and save it to the folder you are using for all of your GIS work for this class.
d. Once you have done that and returned to the Centroids pop-up window, make
sure that the box for “Open output file after running algorithm” is checked and
then click “Run” in the lower right-hand corner.
e. Once you see the Centroids layer appear in your Layers panel (or you see
“Algorithm ‘Centroids’ finished” appear in the pop-up window’s log), you can
close the pop-up window and examine your map. You should see dots in the
center of each state.
f. Now, we can tell QGIS to adjust the size of each circle according to the variable
we want to map, in this case, population. To do this, right click on your centroids
layer in the Layers panel and select Properties and then the Symbology tab.
g. This time we want to keep the drop down menu at the top on “Single Symbol.”
Select one of the “dot” options so that we will see circles on our final map, but
GEOG 360: GIS & Mapping
feel free to adjust the color to your liking by clicking on the color that is there
and adjusting it to your liking.
h. When you are happy with the color, let’s tell QGIS to adjust the size of each dot.
To do this, click on the “Data defined override” button at the end of the line that
starts with the word “Size.” The button looks sort of like a file cabinet with an
arrow on it.
i.
From the drop-down menu that appears, we will select “Assistant…” which will
open a new window called “Symbol size.”
j.
There, we want to set as the Input Source our population variable. Nothing will
happen automatically, but if you then click the “Fetch value range from layer”
button (similar to a refresh button with two blue arrows creating a circle), you’ll
see the range of circle sizes appear in the window on the right.
k. Let’s keep the default settings for now, but feel free to play around with the
relative sizes of your symbols using the options in the “Output” section. Click
“OK” to close the “Symbol size” window.
l.
Now still in the Symbology window there is one more step that is unique to
proportional symbol maps. Typically, you don’t add a legend until you make
your print layout and start positioning things on the page, but for proportional
symbol maps we need to take an extra step to set us up for that. Click on
“Advanced” in the lower right-hand corner and select “Data-defined Size
Legend…” from the drop-down menu. Select the Collapsed legend option and
you’ll see the legend appear in the preview box.
m. Typically, this legend will be a bit too cluttered, so you can simplify it. To do this,
check the box next to Manual size classes and then use the green plus button to
add a couple reasonably-sized (this will depend on the range of the data)
reference circles. If you add one you don’t like, you can highlight it and then use
the red minus sign to remove it. When you are happy with it, click OK.
n. Now go ahead and click OK again to close the Symbology window and return to
your map. You should now see proportional symbols overlaid over your
choropleth map.
7. Now, let’s create one final type of thematic map: a dot density map. Here, we will use
county level data rather than state level data.
a. To make a dot density map, we need to randomly place dots in each county
based on the number of people living there, or the population. To do this click
“Vector” in the menu at the very top of your screen, then select “Research
GEOG 360: GIS & Mapping
Tools” and then “Random Points in Polygons”. This should open a Random Points
in Polygons pop-up window.
b. First, we want to set the Counties layer as our Input polygon layer.
c. Second, we need to tell QGIS how many points to put. To do this, click on the
“Data defined override” button at the end of the line that says “Number of
points for each feature.” The button looks sort of like a file cabinet with an
arrow on it. Select “Assistant” which will bring up a new pop-up window.
d. In the Input box, at the end of the “Source” line, click on the button with the
purple mathematical symbol. This will open an Expression Dialog box. Now, our
map would be way too cluttered if we put a dot for each person, so while we
want to base our dots on population, we want one dot to be equal to one
thousand people, so we will write our formula as follows:
Population / 1000
Once you have done that, click OK. Double check that you have done that
correctly by clicking on the “Fetch value range from layer” (the refresh button
with two blue arrows pointing at one another). You should see a “from” value of
0.066 and a “to” value of 10,081.
e. Now let’s look at the Output box. Right now, we are limiting our ability to
implement that because our output range is only 1-10 (not 0-10,081), so let’s
change it. Set the “Output from” box to 0 and the “to” box to 10081. Make sure
the Exponent is set to 1 and the “Output when NULL” box is set to 0. Then click
the blue arrow next to “Number of points for each feature” to return to the main
pop-up window.
f. The last thing we need to do before adding our points is to tell the computer
where to save the new points layer it is going to create. Scroll down to where
you see [Create temporary layer] and click the “…” button at the end of the line
to tell QGIS where to save your file (ideally in your class GIS folder).
g. Once you have done that click “Run” and wait a minute while QGIS does its
thing. You’ll know it is done when the Log says that the algorithm finished.
Once you see that at the bottom of the log, click close and take a look at your
map.
h. Likely you’ll notice that there are a lot of dots and that they all overlap making it
hard to actually see the patterns. To fix this, right click on your new dot layer,
select Properties, and then the Symbology tab.
GEOG 360: GIS & Mapping
i.
We will keep the symbology on Single Symbol. Pick whatever color you like and
set the size to 0.4. You can adjust the size later if you want, but this is a good
place to start.
j.
When you are done adjusting your symbology, click OK and examine your map.
You have now learned how to make three different types of thematic maps: choropleth maps,
dot density maps, and proportional symbol maps. Using the four map components you made
construct two mixed symbols map. The first should be a state-level choropleth map overlaid
with a proportional symbol map. The second should be a county-level choropleth map overlaid
with a dot density map.
8. Using what you learned in the first skill development lab, make two print layouts (one
for each of your mixed symbols maps and add the map image, a title, and a legend to
each. You are welcome to just show the contiguous United States (the lower 48 states)
if you wish.
9. Take some time to play around with your map element’s settings. You can adjust the
font and size of your title and adjust a lot of the specifics of your legend. To do this,
select an item from the Items list on the right-hand side of your print layout and then
use the Item Properties tab just below it to make adjustments. Remember to pay
attention to the visual hierarchy of your map! Everything on your map should be
contributing to communicating how the population of the US is distributed.
10. As you did in Lab 1, once you are happy with your maps, export each of your two maps
and submit them using the Lab 2 submission portal. You will be assessed using the
rubric below on both whether you completed each of the map components and the
effectiveness of your map at communicating information.
Skill Development Lab 2 Rubric
Criteria
Map 1
Ratings
10 pts.
Mixed Symbols
Map
(Choropleth &
Proportional
Symbol)
Map submitted,
includes a
proportional
symbol map
over a
choropleth map
with an
appropriate title
and legend.
7 pts.
4 pts.
0 pts.
Map submitted,
shows clear
effort, but does
not include all
required
elements.
Map submitted,
but lacking
either the
choropleth or
proportional
symbol
component.
No map
submitted.
GEOG 360: GIS & Mapping
Skill Development Lab 2 Rubric
Map 1
5 pts.
3.5 pts.
2 pts.
0 pts.
Choropleth
Component
Choropleth map
component
includes
appropriate
color ramp and
is symbolized
effectively in the
legend.
Choropleth map
component
shows effort,
but is not
effectively
executed.
Choropleth map
component is
absent.
Map 1
5 pts.
Color ramp is
used and legend
includes
choropleth
symbols, but
could more
effectively
communicate
the information.
3.5 pts.
2 pts.
0 pts.
Proportional
Symbols
Component
Proportional
symbol map is
correctly
implemented
and is
symbolized
effectively in the
legend.
Proportional
symbol map
component
shows effort,
but is not
effectively
executed.
Proportional
symbol map
component is
absent.
Map 2
10 pts.
Proportional
symbols are
present and
represented in
the legend, but
could more
effectively
communicate
the information.
7 pts.
4 pts.
0 pts.
Mixed Symbol
Map
(Choropleth and
Dot Density)
Map submitted,
includes a dot
density map
over a
choropleth map
with an
appropriate title
and legend.
5 pts.
Map submitted,
shows clear
effort, but does
not include all
required
elements.
Map submitted,
but lacking
either the
choropleth or
dot density
component.
No map
submitted.
3.5 pts.
2 pts.
0 pts.
Choropleth map
component
includes
appropriate
color ramp and
is symbolized
effectively in the
legend.
Color ramp is
used and legend
includes
choropleth
symbols, but
could more
effectively
Choropleth map
component
shows effort,
but is not
effectively
executed.
Choropleth map
component is
absent.
Map 2
Choropleth
Component
GEOG 360: GIS & Mapping
Skill Development Lab 2 Rubric
Map 2
5 pts.
Dot Density
Component
Dot density map
is correctly
implemented
and is
symbolized
effectively in the
legend.
communicate
the information.
3.5 pts.
Dot density map
component is
present and
represented in
the legend, but
could more
effectively
communicate
the information.
2 pts.
0 pts.
Dot density map
component
shows effort,
but is not
effectively
executed.
Dot density map
component is
absent.
GEOG 360
Lab 2: Mapping US Population
GIS and Mapping
TA: Ben Trumble
Office Hours:
Thursday,
3:30-5:30pm, zoom
Tuesday // Thursday
Section AA : 1:30-2:20
Section AB : 2:30-3:30
Question of the Day:
What is your favorite
weather?
To Email
Me… “I’m
Just Ben”
Lab 2 Objectives
The geographic question to be explored in lab:
○ How is population geographically distributed
across the United States?
●
●
Choose symbolization strategies that align with the argument
the map is making
Match the visual hierarchies on the map with the intellectual
hierarchies of the map’s argument.
My cat Yucca, unfortunately
distributed directly in front of
the TV.
Thematic Maps Overview
Choropleth Map
●
●
A symbol or marked and
bounded area on a map denoting
the distribution of some property.
Uses intensity of color to
correspond with an aggregate
summary of a geographic
characteristic within spatial
enumeration units, e.g.,
population density or per-capita
income.
Create and use a choropleth map—ArcGIS
Insights | Documentation
Dot Density Map
Proportional Symbol Map
●
●
Show relative differences in
quantities among features.
Proportional symbology is similar
to graduated symbols
symbology
Reflect on quantitative values
Proportional symbols—ArcGIS Pro |
Documentation
●
Each dot represents a constant
number of things, people, or
other quantifiable phenomena.
The dots are equally sized, even
when multiple fields are
symbolized together in a layer.
Dot density—ArcGIS Pro |
Documentation
By Popular Demand: Quick Symbology
Data Wrapper Academy
Hands on Data-Visualization
More on Choropleth
Use the Smallest Units Possible
Think about the legend
Make sure that
readers see all
the differences in
the data. Make
sure to use data
breaks (jenks vs
quantile, etc) to
make regional
patterns visible,
but not to overly
blow up the
difference
between regions.
Check out the article these come from:
What to consider when creating choropleth maps
Where art and data can intersect
Explore More!
Articles/BlogsTake Care of your Choropleth Maps
DataWrapper Coloblind Series 1,2,3
How to pick more beautiful colors for your data
visualizations
Design Choropleth Colors & Intervals
Your Friendly Guide to Colors in Data Visualisation
ToolsColorBrewer
Datawrapper
Google Art Palette Experiment
Colorpicker for data
Data Color Picker
Elements of A Map
1. Title
(All Capitalized and Spelled
Correctly)
2. Data Frame (s)
(the map, sometimes 2-3)
5.
3. Legend
(#’s rounded, description)
North
Arrow
6. Scale Bar
7. Citation
Box/
Metadata
(source,
4. Neatline/Frames
Screenshot of QGIS print layout
projection,
name, date)
GEOG 360
Lab 2: Mapping US Population
Create a choropleth map
GEOG 360
Lab 2: Mapping US Population
Generate centroids of
polygons
GEOG 360
Lab 2: Mapping US Population
1.
Make centroids into proportional
symbols
2. Collapse the legend
GEOG 360
Lab 2: Mapping US Population
WRONG way to create
proportional symbol map
Proportional symbol map is
different from choropleth
map. On a proportional symbol
map, the size of the marker
keeps changing as the value
increasing. It’s a continuous
process instead of discrete one,
therefore different from
classifying.
GEOG 360
Lab 2: Mapping US Population
Create a dot density map
Adjust the size
Mix Symbol Maps Examples
SA
MP
LE
Deliverable 1:
A state-level choropleth map overlaid with
a proportional symbol map
LE
P
M
SA
Deliverable 2:
A county-level choropleth map overlaid with a
dot density map
Lab 2 Deliverable : Submit two mixed symbols map made using QGIS.

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