Creating a Map Layout from Start to Finish - Symbology

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Symbology

Symbology can be changed in three different places - the Symbology tab of the Layer Properties, by single left clicking a patch in the Table of Contents, and by right-clicking a patch in the Table of Contents - each one with less control then the one prior. The Symbology tab offers the most choices and should be used almost exclusively if the layer is not being represented by a single symbol (that is, all the features are colored identically and no field is defined). Single left-clicking on a patch (point, polyline, or polygon) in the Table of Contents will launch the Symbol Selector dialog box (click to jump to the explanation of how-to), which allows you to make many changes in the size, color, and style of a single symbol, as well as create your own symbols. Right-clicking on a patch (point, polyline, or polygon) will allow you to change only the color.

Included in Symbology is the ability to change the display labels are displayed within the Categories, Quantities, Charts, and Multiple Attributes.

Click on the type name to jump to the section for a more in-depth explanation and how-to images.

  • Use the Features symbology set for coloring all the features in a layer in the same manner (the default setting when adding a layer to ArcMap
  • Use the Categories symbology set for text or date fields.
  • Use the Quantities symbology set for numeric or currency fields.
  • Use the Charts symbology set to add a pie, bar/column, or stacked chart using two or more numeric fields to each feature.
  • Use the “Multiple Attributes” symbology set for numeric or currency fields where you need to create unique values combining two or more fields.

Other options for adjusting symbology include:

  • Importing the Symbology from one layer to another, assuming they share at least one value in the attribute table to symbolize by

Symbology Show: Menu - Features

The features window will color all of the features the same way. Click on the current symbol to open the Symbol Selector dialog box where you can set the fill color (polygons), outline color (polygons and polylines), or point symbol.

Symbology Show: Menu - Categories

Symbology by Category will allow us to display data based on one or more field. For example, if we want to color each county of Colorado a different color, we can set the symbology to Category, make the value field “County_Name”, add all the values to the list, and set a color ramp. If we wanted to add just a few values to our map, say coloring roads by the number of lanes, we could set the symbology to categories and only add the values for the lane counts we’d like to display.

Unique Values - One Field

“Unique values” will color each feature in the layer based on the attributes found in a single field such as two lane roads colored dark grey while four lane roads are colored red.

Unique Values, Many Fields

“Unique Values, Many Fields” will color features based a combination of two or more fields creating a unique value. For example, a layer containing crime data might have a field for the name of the neighborhood and another with month names and a third with reported armed robberies. There might be then be a feature with a three field combination of “Central Heights, January, 27” and another with a combination of “Central Heights, February, 14”. Even though we see “Central Heights” twelve times, each three field combination creates a unique value, which each polygon can be symbolized by.

Symbology Show: Menu - Quantities

To display your map as an choropleth, isopleth, proportional symbol, graduated symbol, or dot density map, first open the Symbology tab in the layer’s properties. Once there, select “Quantities” from the “Show” menu and choose one of the four options (choropleth and isopleth are both found under “Graduated colors” and differ based upon the classification method).

Choropleth and Isopleth Maps - Graduated Colors

Based upon the frequency distribution of the data, the “Graduated Colors” portion of the Quantities menu utilizes the field’s histogram to set the break values for classification. When we use the “Equal Interval” classification method, the result is an isopleth map, while all the other methods result in a choropleth map.

Graduated Symbol and Proportional Symbol Maps

Proportional and graduated symbol maps represent both geographic location and an attribute value for a single location, utilizing a symbol size to represent either an exact value (proportional) or to represent a class of values (graduated). For example, you could represent both city location and population with a graduated symbol. The symbol will sit at the geographic coordinates (often the city center) and the size of the symbol will represent the population - a small symbol will represent a lower population than cities with a large symbol.

Both proportional and graduated symbol maps can clearly display a message without too much analysis needed on the part of the reader. Large symbol, large number, small symbol, small number. Easy peasy. However, this style of map can quickly get out of control by attempting to place too many symbols on one map, too many symbols in a small geographic area, pointlessly using a representative symbol when a choropleth map would accomplish the task cleaner, or using symbol sizes which are too large or do not have enough distinction between the high and low values. When used with caution and in combination with a choropleth map, proportional and graduated symbol maps can be done very neatly with a powerful, crisp message.

Graduated Symbol Maps

Proportional Symbol Maps

Dot Density Map

Dot density maps are a representative data thematic map, where one dot on the map represents one or more occurrences of a single attribute value. Within ArcMap, you can adjust how many values a dot represents and the size of the dot (small size for large amounts of data and vice versa) for one or more fields. As with all mapping techniques, the amount of dots and how many fields are represented should be based upon the purpose of the map and how the visual outcome will present itself to a reader.

Symbology Show: Menu - Charts

Two or more values can be represented with a chart per feature as a symbology option. For each point, line, and polygon in a layer, a pie, bar/column, or stacked chart. Once the chart has been set, there are options to adjust the size and colors, exclude certain values if they exist in the field but do not pertain to layout, and orientation. Even though the below example displays a pie chart, each of the three chart types will have slightly different options.

From the Table of Contents

Single left-clicking on a patch (point, polyline, or polygon) in the Table of Contents will launch the Symbol Selector dialog box, which allows you to make many changes in the size, color, and style of a single symbol, as well as create your own symbols.

  • Items such as color, outline width, line weights, and advanced symbol editing (via the Edit Symbol... button) can be found here

Right clicking on the symbol’s example below the layer name will open the color selection dialog box. This only allow you to change the color of the selected symbol.

Importing Symbololgy

Often, two or more layers are used to express the same idea in two or more data frames. It would then be necessary to use the same symbology, classification, and legend labels to express the ideas across two or more areas. Instead of attempting to accomplish this by hand, ArcMap offers an option to import the entire symbology definition, just the symbols, or just the classification from another layer.

From the Symbology tab of the in the Layer Properties of layer you want to import to, click the “Import...” button, select the layer to borrow from, and choose what to import. That was easy.