Nominal Data Symbology for Area Data (qualitative)
Base Map data
- Create a folder lab5 in your local directory
- Start a new map file and add data: L:\labs\geog205\thematic_map\water_bodies.shp and river_lines.shp
- Save the map file as lab5.mxd in your local folder
Note attribute values in water_bodies DSCRPTN field: Gravel Bar, Lake, Wetland, River
- Symbolize as Categories the values in the DSCRPTN field, and rename the layer as Water Bodies in Table of Contents.
The large rivers appear as polygons. It is not necessary to differentiate large rivers from lakes. The rivers polygon value can be grouped with lakes as follows:
- Layer Properties -> Symbology tab, highlight both rivers and lakes, right-click the selection and Group.
- On the Symbology tab under the Label field, highlight the grouped value label and re-type the label as Water. Leaving the Layer Properties window open, click the Apply button and examine the results in the Table of Contents.
- Next, in the Layer Properties -> Symbology tab, ensure that the order in which the value labels appear is changed so that Water is at the top of the list by highlighting the label of interest and using the promote/demote black arrows to move the label up or down. The position on this list affects their order in the Table of Contents and in the Legend. OK
- Rename river_lines as Rivers and symbolize accordingly.
This layer was developed so that the center line of large rivers (polygons) is part of the line layer. The Fraser River is the large polygon river running north-west to south-east across the dataset. Zoom in on any part of the Fraser River to a display scale of about 1:60,000 to see these features. To hide the unnecessary centre line within large polygon rivers, change the drawing order so that Rivers draws beneath Water Bodies. Examine the results on the map – zoom to a display scale of about 1:150,000 and pan around.
Once you have finished symbolizing the water features save the symbology (your cartographic instructions) to a *.lyr file to be loaded into your next map: right-click Water Bodies –> Save as Layer File.. to your lab5 folder. Do the same for your rivers layer.
- Add Data: L:\labs\geog205\thematic_map\rshade
In the raster’s Layer Properties -> Symbology tab, change the stretch type to Minimum Maximum to lighten the shading.
You can see that this area encompasses mountains and a broad valley running north-west to south-east: the Rocky Mountain Trench. The mountains to the north-east of the Trench are the Rocky Mountains. The mountains to the south-west of the Trench are the Caribou Mountains. The entire dataset covers about 30 km from east to west. You can confirm this by using the Measure tool.
- Save changes to your map document.
- Turn off the shaded relief so that it does not draw in data view.
- Rename the Data Frame to Goat River.
- Add Data: L:\labs\geog205\thematic_map\forest.shp
First, you will symbolize this layer by the primary tree species codes found in the field SPC1_CD_1. This is a nominal category. Examine forest’s attribute table to see this field.
- In the Symbology tab, symbolize all the values in SPC1_CD_1 as Categories –> Unique Values using the SPC1_CD_1 field.
- Select the Add all Values button and apply
- Clearing Up Visual Clutter: Creating a Visual Merge
- In forest -> Layer Properties –> Symbology tab, click on the Symbol heading and select Properties for all symbols. Make sure you have selected Properties for all symbols.
- Set outline to none. (Apply). This will also remove the internal boundaries of the map tiles (TRIM 1:20,000) that make up this data layer.
Examine the spatial data. With the polygon outlines removed, contiguous polygons of the same value (same primary tree species) are visually merged. Removing the outlines in this context has reduced visual clutter (unnecessary detail for the objectives at hand – the polygon outlines could be useful in another context).
The entire data set contains 18 tree species and subspecies. The following table explains the original codes in the dataset.
|AT||Trembling Aspen||Populus tremuloides|
|BL||Subalpine Fir||Abies lasiocarpa|
|CW||Western Redcedar||Thuja plicata|
|EP||Paper Birch||Betula papyrifera|
|HM||Mountain Hemlock||Tsuga mertensiana|
|HW||Western Hemlock||Tsuga heterophylla|
|PA||Whitebark Pine||Pinus albicaulis|
|PL||Lodgepole Pine||Pinus contorta|
|SB||Black Spruce||Picea mariana|
|SE||Englemann Spruce||Picea sp|
|SW||White Spruce||Picea glauca|
|SX||Spruce X||Picea glauca x sitchensis x engelmannii|
In order to simplify the colour palette, you will next group similar trees.
- In the Symbology tab, hold down the CTRL key and highlight codes that you will be grouping into one class.
- Right-click your mouse over the selection -> Group. Under Label change the label as described below.
Continue to group & re-label the following:
|AC and AT||Broadleaf|
|S, SW, SE and SX||Spruce|
- Click Apply
- Save changes to the map file.
In order to improve map readability, a strategy for the order of the value labels in the Table of Contents would be to have the codes listed in order of decreasing area. The area can be guessed by the Count field (number of polygons per class).
- In the Symbology tab, if there are no values showing at this time, click on the Count field.
- Change the order from highest to lowest count. The number of polygons may not be a perfect way to guess total area for a species code, but it is close enough. If you notice discrepancies, you can change the order later.
- Click OK.
Examine the colours on the map and compare them to the codes in the Table of Contents. It can be easier for the map reader to notice the colour covering the largest area. If that colour is labelled first on the Table on Contents (and later the legend), the map reader quickly determines the meaning of the colour. If the map reader has to scan down the list, this will take longer.
There is one exception. Since this is a theme of tree species, the value for non-treed (<> ) should be moved to the bottom of the list. Change this label to Non-Treed and make it a pale gray fill with no outline. Examine the map data view.
Check your drawing order in the Table of Contents. The forest layer should draw beneath water bodies and rivers.
Choosing Colours for Nominal Data:
Colour Philosophy: The basic approach to symbolizing nominal categories is to use random colours: no colour within the group should advance (“pop” out). It is important that no two colours chosen for the symbol set are too visually similar. In a complex map with great detail this would make it difficult to tell polygons apart. First, because the human brain can’t retain the visual information long enough while looking from the map colour over the legend and back again to discriminate similar colours. Second, the colour of a polygon when surrounded by other colours experiences a colour shift which compounds the colour matching problem between the legend and the map polygon fills. A third complication arises as a colour on a computer monitor is flooded from behind by the screen’s light and that same colour on a paper print is created by pigments on a page reflecting light. A single colour can look different based on its medium. This may cause a computer monitor designed colour to look darker on the printed page (or paler) than intended, and may cause two or more colours to be difficult to visual discriminate on the printed map and match to the legend.
Do not use darker shades of one colour in a nominal symbol fill set (for example, multiple shades of green) since increasingly darker shades of one colour is used to symbolize magnitude (interval) data as “darker” means “more”.
For this exercise you will use polygon fills, do not use patterns.
Developing Meaning for your Colour Tints:
Colours can be associative, e.g. blue for water, green for forest. In the case of tree species, associative colours could be designed based on an understanding of the tree species themselves.
Western Cedar and Hemlock belong to the Rocky Mountain Trench’s Interior Rain Forest. Douglas Fir in the Trench in this context are usually part of the Interior Rain Forest. The rainforest is rich in tree vegetation and is much older than surrounding forests. Broadleaf is at the valley bottom, has a longer growing seasons, is wetter and flatter and its ecology tends to be more productive for some kinds of wildlife. Subalpine Fir is usually found in this context at high elevations immediately below treeline where the growing season is shorter and the climate drier and cooler. Pine is usually younger, and drier than the other tree species. Black spruce is usually found bordering wetland settings and is itself comparatively boggy. Paper Birch is similar to the broadleaf class.
As such, you can think of colour tints representing cool colours, or warm colours, more rich colours etc. to generally match the ecology of the trees. This can be for your first choices, and may not be necessary for all the species as you might run out of tints that you can tell apart on the map, and that you can match to the legend.
If you run out of ideas for tints, reserve using colours with greater saturation for areas of limited areal extent on the map. Visually, Douglas fir, Black Spruce, Paper Birch and Pine each take up smaller areas on this map. To test this, for each of these four species in turn, try turning the symbol colour to red so that you can easily see the species limited areal extent on the map. Then choose an appropriate colour. You choose the more saturated colour when you can no longer create a tint that contrasts with the other tints you have already chosen. Remember, the technique of giving a more saturated colour to smaller areas should not make the smaller area “advance” too much.
Here is a reminder of how to change the specific value of the colour:
In the Symbol Selector:
|Click the drop-down arrow beside the Fill Color, and click More Colors..|
|You will see the Color Selector.Click the black arrow and select the colour model HSV.You may now adjust an individual colour.Note that as you change the HSV numbers, the preview colour box on the left changes.|
Ensure the percentage of gray for Non-Treed (the V of HSV) is 97%
The number of colours you will now design has been reduced from 18 to 9. The theme is dominant tree species.
Proceed now to assign tints to the 9 classes. Ensure you:
- can distinguish the tints (you can tell them apart visually),
- can match a colour fill on the map to its patch on the Table of Contents
- do not allow any colour to “advance” – that is, no colour is dominant.
If you find that a colour is visually dominant, you might find that assigning it to a tree species that covers a small area on the map may improve the visual balance.
- You can save this map as nominal.mxd
- Save your map document.
Draping Nominal Symbology over Shaded Relief:
- First, turn the forest layer off in the Table of Contents, and turn the shaded relief rshade on. As you examine the shaded relief you will see shades of gray.
The following illustration shows a strip of the shaded relief A. One colour is placed over that shaded relief in B. The same colour is given a transparency of 40% in C.
|The gray value of the colour sample in B varies throughout C.You should be aware that drapes create variation within your original colour choice.|
- Turn Forest back on so that it draws.
- Create the drape: Forest’s Layer Properties -> Display tab, set the layer’s Transparency to 40%.
Examine how much variation now exists within any one of your chosen colours.
- Remove the transparency value – ensure it is set back to 0 in the forest layer.
- Turn off the shaded relief so that it does not draw.
- Save the map file to nominalhsd.mxd under your lab5 folder.
Symbolizing Areas by Quantities
- Start a new map, toggle back to the Data View, and add data from your lab5 folder:
water_bodies.lyr and rivers.lyr
- Save your map document to your lab5 folder as quantities.mxd
- Add Data L:\labs\geog205\thematic_map\forest.shp
- Open its attribute table and note the two fields. SPEC_CD_1 represents the primary tree species in the polygon. Age_1 represents the age in years of that polygon.
- Symbolize Age as Quantities -> Graduated colors
- Select an appropriate color ramp and apply
You will see numbers from 0 up to 450 years in the Table of Contents.
Look for pattern in the map. Can you determine the age of the polygon on the map visually? You can query the polygon with the Identify tool. To improve the visual quality of the map, you should remove the polygon outlines (as in section 1). It also removes the unwanted map tile edges. Try this now.
While magnitude is shown as increasingly dark colours, there are too many values in the dataset resulting in too many colours. It is not possible to match a colour to the legend, nor discriminate between the numerous colours on the map. Plus, the gaps in the data values are not illustrated properly as the colour change is continuous. Remove the 0 value colour patch from the Symbology tab. This doesn’t improve visual quality.
You could improve the discrimination by changing from a one-colour blend to a two-colour blend. Try a suitable two colour (bichromatic) ramp if you haven’t already.
Apply this to the map. Examine the results.
What will prove to be helpful will be a generalization of the range of data values. To do this, you will next classify the age values.
- In the Properties -> Symbology tab (it should still be active)
- What classification method is being used?
- Click the Classify button and examine the histogram. What is a histogram?
Since a polygon with the value of 0 is a treeless polygon, you will now exclude it from the classification:
- Click the Exclude… button and enter the following expression into the query window, by double-clicking on AGE_1 and single clicking on = and then typing 0
“AGE_1″ = 0
- Click OK, return to the map and examine the results of this classification on the map. [The default palette was a two-colour blend (yellow to brown)].
Notice the range of class values in the table of contents (for example, all years from 1 to 53 are grouped into one class, and assigned the colour pale yellow). (these numbers may not exactly match yours) Notice the upper value of the class ranges: ~ 53, 125, 187, 246, 450.
Keeping the same palette experiment with all the classification schemes discussed in lecture: Natural Breaks, Geometric, Equal Interval, and Quantiles. You should also experiment with changing the class number from 5 to 7. You will leave the map in Data View. Make sure you have removed the polygon outlines.
Lastly, create User-Defined Classes using the following classification scheme:
|1||1 – 20 Years|
|2||21 – 40 Years|
|3||41 – 60 Years|
|4||61 – 100 Years|
|5||101 – 140 Years|
|6||141 – 250 Years|
|7||251 + Years|
- Save this as age_class.mxd
Assignment #2: Due Friday Feb. 23th (4pm)
In this assignment, you are required to produce two maps:
- Nominal map of forest data with hillshade background
- Quantity map for forest age classified in this lab
Both maps should be
- well layout with proper title, legend, scale bar, your name and data.
- Letter page format 8.5 x 11 “
- Colors permitted
- Legend with a suitable sample number of symbol sizes
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.
- Export the nominal map as lastname_firstname_geog205_as2_nominal.pdf
- Export the quantity map as lastname_firstname_geog205_as2_quantity.pdf
- Send the file to your TA by email with subject “Geog205 AS2″