In this lab, we are going to use population data for northern BC towns and cities to practice the symbolization with graduated symbols and proportional Symbols. Please check lecture for the concepts of range graded and proportional symbolization
The spatial data we will be using for this lab are located at L:\labs\geog205\thematic_map
- Create a new folder thematic_point under your geog205 folder,
- Open a new map document and add the layers above
- Set up the layers in a fashion that shows all the points of the Northern BC towns, the portions of the BC highways and the provincial boundary that will fit at a scale of 1:5,000,000
- We will change the symbology of the point layers through the lab
The northern_towns_pop_2000_2011_2016 layer’s attribute table has fields depicting the population numbers for each town from the years 2000, 2011 and 2016. The table also shows the changes in population for the three time periods, but we are only interested in the changes from 2011 to 2016 in this lab (click the image to see large image)
You can see columns with the population numbers for each year as well as columns for the changes from one year to another (i.e 16_11 represents the changes from 2011 to 2016). What do you think the columns with the prefix “type” in the columns header (i.e “type_16_11″) represent. HINT: why are all the values in the columns positive numbers?
In order to reduce the clutter in the attribute table and to focus on the task at hand (the changes from 2011 to 2016), you are going to hide some of the extra fields. To temporarily turn off some of the attribute table fields:
- Right click the northern_towns_pop_2000_2011_2016 -> Properties -> Fields tab. All visible fields have a checkmark.
- Click the Clear All button to remove all the checkmarks, and place a checkmark for the following five field names: NAME, POP_2011, Pop_2016, 16_11 and type_16_11
Re-examine the attribute table. You should now see that all the non-checkmarked fields are hidden from view. The attribute table remains unaltered, all its data remains on the hard drive and the instructions to hide the fields from your view are stored in your map document.
Now is a good time to save your work by the way!! Maybe something like thematic_point.mxd.
Examine the attribute data more closely:
- You can get a better understanding of the data by right clicking on the field titles (headers) and sorting the field data
Q: Which communities have the larger numbers for population change ? How about the relationship between the changes in respect to town population for 2016?
Scanning attribute values in a table is informative, but a spatial representation of the locations, place names and magnitude of population changes on a map is a powerful graphical method of data representation.
1.Range Graded & Graduated Symbols
The remainder of this lab will be spent in designing a map that incorporates ‘graduated’ symbols. When working with graduated symbols consider the following:
- Symbol size measured in area should reflect the values being represented.
- All symbols should be visible. The smallest symbols should be bigger than dots.
- There should be some overlap to give the impression of concentrations in some parts of the map.
- Where there is overlap, the smaller symbols should retain their outline to give the visual impression of being on top
- The circle is the standard graduated symbol, but in some cases, other shapes may work better.
For ArcMap Graduated Symbols (Range Graded):
- If it is necessary to class or group the values (ArcMap graduated symbols), values should be grouped for maximum similarity within the classes and maximum variation between the classes. Class boundaries, should where possible, be round numbers (10, 50, 100 etc).
ArcMap: knowing the difference between literature and software terminology
- Graduated symbols are known as Proportional symbols in the ArcMap software
- Range graded symbols are known as Graduated symbols in the ArcMap software.
- Memory tip: range graded = graduated
- For the remainder of the lab, ArcMap terms will be used
ArcMap Graduated Symbols
- Set the Data Frame Properties -> General tab Reference Scale to 1:5,000,000
- In northern_towns_pop_2000_2011_2016s -> Properties-> Symbology tab, and click on Quantities.
- Click Graduated Symbols (remember that this selection represents the range -graded symbols from lecture)
- Click the dropdown list for Value Field and choose 16_11.
- You will find these symbols are too small, and may be a poor color.
- To change, change Symbol Size range, set the upper range to 40 and the lower to 8. Click OK.
This shows the changes in Population.
Try the same methods to see how these points look when you are investigating populations values (i.e use POP_2016 for the Value field).
- Change the value field back to 16_11 before going to the next section.
Arcmap ‘graduated’ symbols (described as range graded in lecture)
Let’s evaluate what the software has done. To do this, focus on two of the points representing area, lets use Prince George and Fort Nelson.
To focus on these two locations in the map, go to northern_towns_pop_2000_2011_2016 -> Properties -> Definition Query tab. Whatever attribute value is found to be true in the query written here will be the feature drawn on the map. All attribute values that are false are hidden from view.
Build the following query with Query Builder.
“NAME” = ‘Fort Nelson’ OR “NAME” = ‘Prince George’
- Click OK.
Turn on northern_towns_pop_2000_2011_2016 labels. To remind yourself of the change in number of students from each area, add the 16_11 value to the label as follows:
- In northern_towns_pop_2000_2011_2016 -> Properties -> Labels tab, click the Expression button.
- Build the following query with Query Builder.
[NAME] & “-” & [16_11]
- Click OK
Before we investigate the results of the symbols;
Can you describe how the expression above produced the labels for the two locations?
We will be using more expressions (little scripts) further in the lab. These scripts can be handy for symbology in ArcMap, so a bit of an understanding is helpful. Using scripting for your projects is not required, so if they frustrate you – you have other options.
How do the numbers compare between the two areas? Do the size of the symbols match the numerical values? It may be easier to evaluate if the shape were a square and not a circle.
- Return to the layer Properties -> Symbology tab and click on the Template button. Choose the green square.
Graduated symbols group the quantitative value into classes (range graded). All values within that class range are drawn on the map with the same symbol. You cannot tell the value of the individual map circle/square symbols, you can only match the circle/square to the range symbol in the legend to determine the possible range of values.
- What is the class range for Prince George?
- Does the circle/square for Prince George match the circle/square in the Table of Contents for that class range?
- What is the class range for Fort Nelson?
- Again, does the circle/square for Fort Nelson on the map match the circle/square in the Table of Contents for that class range?
Graduated Symbols (range graded symbols) select one symbol size for the entire range of values for each class, and as a result, you cannot determine the magnitude of individual town/city values from the map symbol, you can only match the town/city symbol on the map to a class range.
ArcMap Proportional Symbols
ArcMap ‘proportional’ symbols (described as ‘graduated’ in lectures)
- Change the symbology method to Proportional, Value field to 16_11, Unit to unknown and Min Value to 20.
Do the sizes (area) of the symbols (circle or square) appear to be proportionally represented?
ArcGIS Proportional symbols precisely represent the value’s magnitude.
Let’s examine the rest of the Northern towns and cities again:
- Remove the query in the Layer Properties -> Definition Query tab. OK.
- Turn the labels off
- in the Properties -> Labels tab, click the Expression button change the labeling expression back to [NAME] (Highlight the existing expression and then click the NAME value on the upper panel)
- On the Symbology tab, change the Min Value to 4 , and the number of symbols for the legend to 5. OK
With ArcGIS Proportional Symbols, the area of the map symbol represents the specific value for that map symbol, but there are a many sizes to visually interpret. Experiment with the Min Value (for example try 6 or 8). Change the value back to 4.
Having experimented with both techniques, now save you map document as thematic_point_proportional.mxd.
Remember that the Reference Scale makes a huge difference on the sizing of the symbols on the map. You have it set at 1:5,000,000. If for example, you had begun the map with a 1:2,000,000 reference scale, then the sizes would be very different and you would choose different values in the symbology tab to achieve the correct cartographic look for the circles. As you design your proportional symbol map, you have the option of changing the reference scale (you don’t have to). Remember to achieve the cartographic principles discussed in lecture for this symbol technique.
- You should be able to identify a range graded symbol or proportional map when you see them (literature term)
- You will be questioned based on the terms from literature.
- You should also know the ArcGIS equivalent term.
2.Symbology using Multiple Attributes
Graduated (ArcGIS) range graded (literature)
Remember, we are working with changes in population, not actual population. However, you are welcome to play around with population values – or the relationship between the amount of change in to population values. There are many ways to create thematic maps from data such as this dataset (available to students from BC Stats or Stats Canada). We are only showing some methods.
We are using the changes in population and whether population increased or decreased for each town or city. Lets look at the table in it entirety again (add all the fields back to the table for use to view). Which field do we use for indicating a positive/negative change in population – and which value represents positive/negative?
ArcMap Symbology using Multiple Attributes
General procedure for symbology using multiple fields:
Colour the type of change
- Layer Properties -> symbology tab -> Multiple Attributes -> Quantity by Catagory.
- Value field is type_16_11
- Click “add all values” to add 0 and 1 values to the symbology frame
- Click off the “all other values” box in the symbology fram
- label EACH field differently –> value 1 as Positive Change -> value 0 as Negative Change
- Change the colour of the values –> 1 coloured green and 0 coloured red
Setup symbol size
- In the same window (multiple attribute) select the symbol size window
- use the 16_11 field
- 6 classes
- symbol from 10 to 60
You now have a representation of the changes in Population and whether it is an increase or decrease in enrollment
Save your map as thematic_point_population_change_category.mxd
Proportional (ArcGIS) Graduated (literature)
ArcMap does not provide a method of proportional symbolization with multiple attributes, but there is a simple way to get around this. We are simply going to use the same dataset twice, but symbolize the two layers slightly different.
You should still have three layers in your map: BC boundary, Highway layer and the northern town population layer. We are going to reset the map to have proportion symbolization for the northern_towns_pop_2000_2011_2016 layer.
If your thematic_point_proportional.mxd worked out well for you, re-open it (File –> Open –> navigate to the file).
If you are not happy with the file, then re-set the symbology to proportional as we did above with a few more steps:
- Properties –> Symbology –> Quantities –> Proportional Symbols using the 16_11 field
- Leave Units as Unknown
- Min Value is set at 4 and the colour should be red
- As before – use 6 classes
- Exclude Data; Data panel –> Exclude –> type “type_16_11″ = 1
The map now has proportional symbology for towns and cities that have a decline in population for 2011 to 2016. Lets provide the towns and cities with positive change.
Rename this layer in the Table of Contents to something like Northern Towns Decreasing
Add the northern_towns_pop_2000_2011_2016.shp file into the project again (we now have the shape file loaded twice) and rename it Northern Towns Increasing. Once the file is in we can use the symbology from the first northern_towns_pop_2000_2011_2016 layers, and adjust it somewhat.
Right click on the increasing layer:
- Properties –> Symbology –> Import –> Choose the decrease layer –> keep using the 16_11 field
- Change the colour to green (keep the min value at 4)
- Exclude Data; Data panel –> Exclude –> type “type_16_11″ = 0
Make sure the decrease layer is above the increase layer in the TOC (why?)
3.Adding Text Labels
When you turn on the labels for the Northern Towns Decreasing layer, you can see that there are too many overlapping labels. There are ways of solving this problem. For instance you use expressions (as you did above with the definition query) to provide rules based on attribute values. You are welcome to try this – with help…
For the purpose of this lab, try to see if placement can help out
- Open the labels tab from the properties of the layer (Northern Towns Decreasing)
- Click on Placement Properties
- Change location – find and select “Prefer upper right, then Top Then Right
- Conflict Detection tab – set both label weight and feature weight to high
Below we will show you two methods for adding labels
Labeling – reduce your number of features and use creative labels
If you tried the above method, remove the third version of the northern_towns_pop_2000_2011_2016 layer you used to practice with
Reduce the number of labels
You can begin to pare down the number of labels by labeling only the cities/towns that have a change in population change greater than 1000.
Create a query within the labeling expression that limits labels to those features with a population change value greater than 1000 as follows:
In Northern Towns Decreasing -> Properties -> Labels tab -> Expression button, the expression is presently [NAME].
- Place a checkmark for Advanced Expression and delete everything there.
- High-light the entire expression in the Expression window – should be [NAME], and delete it (right-click selection – Delete)
- Copy and paste the following expression into the Expression window:
Function FindLabel ( [NAME], [16_11] )
if [16_11] > 1000 then
FindLabel = [NAME] & vbnewline & [16_11]
- Click OK and OK again to return to the map to view your results.
- Adjust the label text size
Now label Northern Towns Increasing layer in the same way
When you right-click a feature layer in the Table of Contents and turn Label Features on as you have done, you are creating Dynamic Labels. Dynamic Labels are being read directly from the attribute table. The default setting for the software is dropping conflicting labels. You have no control over which of the northern cities are being labelled. You can force all labels for features to draw as follows:
- Layer Properties -> Labels tab -> Placement Properties button -> Conflict Detection tab and place a checkmark at the bottom for Place overlapping labels.
Examine the results on the map. This creates a lot of overlapping labels.
You can also add a halo to your labels by:
- Allowing overlapping labels – unchecking Place overlapping labels
- In Northern Towns Decreasing -> Properties -> Labels tab –> Symbol button –> Edit Symbol –> Mask tab. Click on Halo and set the size (thickness) to 1 or 0.5 points ( you can play around with this of course).
- Keep clicking OK to finish.
You can do the same for the Northern Towns Increasing layer
Save the map file to thematic_point_proportional_up_down.mxd
Example of some playing around with labels
There are many other options for labeling. For instance, if you are looking to create labeling similar to the map below, you can follow these steps:
- Return to the Labels tab and click on the Symbol button
- scroll do the list of symbols and select the Banner Text, Rounded style
- once selected, click Edit Symbol –> Advanced Text
- turn on Text Background and click its Properties
- turn on the lower balloon callout and then the Symbol button beside it
- select a colour that is slightly darker than your colour for the BC Boundary
- Click all the OK buttons until you are back at the Layers Properties Panel
- Hit Apply and OK again
- Voila labels as below
More to consider for your map
Labeling the smaller population change towns
It is a good practise to save your map before you try other actions that may change your map in a way you do not prefer – save your map again perhaps using a version number perhaps:
If you study your map closer, you can see that you do not know the names of many of the towns. There is also confusion around the precise location of of the towns especially for the overlapping proportional symbols (eg. the Peace area – Taylor and Ft St John. The steps below can be employed to add in point locations of the towns as well as adding the labels. The method below also requires some manual editing of label locations (after converting labels to an annotation layer).
Add in the northern_towns_pop_2000_2011_2016 layer one more time (three versions of the layer in your table of contents). Set your scale in the layout view to 1:5 000 000 and centre your map in such a way to promote the northern half of the Province (setting the focus of the map on the northern towns).
Change the position of the label relative to the feature point as follows:
- Symbology –> single symbol –> colour –> no colour
- Labels tab -> Placement Properties button –> Place label on top of point –> OK
- make sure your label field is NAME –> click apply
- check your output and adjust your style accordingly (i.e. you can apply halos etc)
- Close properties box
Save your map again – i.e thematic_point_proportional_up_down_labels_v2.mxd
- Right click on the new layer in the table of contents –> convert labels to annotation –> store annotation –> in the map
You now have unattached labels (as we did by converting the legends to graphics in the last lab). You can use the pointer in ArcMap to grab the labels and move them within the map to place them where you prefer. The labels however, cannot be removed in the same manner as a layer,
4. Assignment #3: Due at the beginning of next lab session (Feb. 12 – 15)
The goal of this assignment is to produce a finished map showing the populations changes for northern towns and cities, using the proportional symbols (i.e. no range graded classes). This should be designed with:
- Letter page format 8.5 x 11 “
- Colors permitted
- Legend with a suitable sample number of symbol sizes
- Suitable background layers for context if necessary (e.g. roads, BC boundary. Background layers not required in legend if explained on the map
- Label a set of towns that have significant changes (you decide this criteria)
- Scale bar
- Suitable title and your name and date.
Note that ancillary information should be fitted around the map, such that the map has visual prominence and area, and the ancillary information is secondary.
The map area itself should fill the page as much as possible, to enable maximum details to the symbols
- Export your map as lastname_firstname_geog205_AS3.pdf
- Send your PDF file to your TA by email with subject “Geog205 AS3″
An example map
Below is a map Scott knocked out. The project involved having the northern_towns_pop_2000_2011_2016 layer loaded into the table of contents 4 times. Two for labeling and positive and negative changes in population proportional (graduated) symbolization, a third for the unfilled circle representation of the proportional change (used for the legend – not on the map), and a forth for a center point for each town and finer control of labeling. This type of map can take some time.
The map below was created in ArcMap. The map can be exported as a SVG or PDF and brought into a graphics package such as Inkscape for further improvement. If you are a real keener – Inkscape is installed on the Linux computers as well as on osmotar.