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QViewer Symbology

QGIS is generally the easiest platform for curating symbology, so it's where I would recommend starting when creating or updating any symbology. Here you'll find step by step instructions for curating symbology in QGIS.

How-to Create a (.qml) File

  1. Open the properties pane for the layer you want to symbolize. You can do this by either double-clicking the layer in the Layers pane or by right clicking your layer and selecting Properties. On the left side of the pane, switch to the Symbology tab.
  2. Symbolize the layer to your liking. See the Symbology Basics section for more detailed instructions.
  3. At the bottom of the symbology tab, there is a dropdown button that says Style. Click the dropdown and select Save Style... which will open the Save Layer Style pop-up.
  4. Click the three dots to the right of File and choose where to save the file, as well as give it a name. Naming should reflect what's being referenced in the Business Logic.
  5. Click OK.

To test your newly created .qml file before adding it to a pull request...

  1. Add another instance of your layer to your QGIS project (you could also duplicate your layer and switch the symbology type to Single Symbol).
  2. Open up the Symbology tab of the properties pane.
  3. Click the Style dropdown at the bottom, and select Load Style...
  4. Navigate to your saved .qml file using the three dots to the right of File.
  5. Click OK and verify that the symbology looks how you intended.

QGIS Symbology Basics

The first step to symbolizing a layer in QGIS is to choose the symbology type. The dropdown at the top of the Symbology tab has options for no symbol, single symbol, categorized, graduated, and rule-based. You're most likely going to be creating categorized or graduated symbology, so those will be described first, followed by rule-based symbology.

  1. After selecting your symbology type, click the Value dropdown to choose which attribute is being symbolized.
  2. The next dropdown is used to make top-level edits to all symbols in that layer. If the symbology you're creating has common traits across classes, you can apply those here to save time. Click the rectangle next to Symbol to open the Symbol Settings pop-up (you can also click the dropdown arrow on the right side and select Configure Symbol...). Here, you can set color opacity and sizing options (line width, circle size, circle outline width, polygon outline width, etc...). Click OK when you are finished to apply changes and return to the Symbology tab.
  3. Use the green + button to add however many classes you need. If you need to remove a class, select the class so that it is highlighted and click the red - button.
  4. Set the values and legend labels for each class.
    • For categorical symbology, double click in the Value column for each class and type in the attribute value. This is case sensitive so double-check that your entries are accurate for the symbology to work! Legend labels are also edited by double clicking in the Legend column and typing your label.
    • For graduated symbology, double click in the Values column to open the Enter Class Bounds pop-up. Type in the upper and lower values for each of your classes. Edit the legend labels by double clicking the space in the Legend column and typing your label.
  5. Edit the symbols for each class by double clicking the symbol in the Symbol column to open the Symbol Selector pop-up.
    • This pop-up is also accessible in the Layers pane the same way (double clicking the symbol)
  6. You will automatically be set to the top-level symbol editing, which will say Marker, Line, or Fill, depending on your geometry type (point, line, polygon), where you can edit color, as well as size (point) or width (line).
  7. To access more symbol options, click the line underneath Marker or Line or Fill that says Simple Marker, Simple Line, or Simple Fill. Here, you have access to more options, such as stroke (outline) color and width for points and polygons, as well as dash patterns in stroke style for all three geometry types.
  8. Keep in mind, after finishing with the Symbol Selector pop-up, click OK (or ENTER on your keyboard) to save changes, or Cancel (ESC) to discard changes.
  9. Back in the Symbology tab, click Apply to apply your changes while keeping the Properties pane open, or click OK to apply changes and close the Properties pane.

Bonus Tip: You can copy and paste symbols within and between layers! In the Properties or Layers pane, right click on your symbol and click "Copy Symbol", and then right click your destination symbol and click "Paste Symbol". This only works if you are copy and pasting within the same geometry type. See the Color Editing section for how to copy and paste colors, which works within and across geometry types.

Color Editing

QGIS provides a lot of options when it comes to color selection, so they get their own section!

  • In the Symbol Selector pop-up, click the arrow dropdown to the right of Color to...
    • Choose a color using the color wheel
    • Set opacity in the box beneath the wheel
    • Copy the current color
    • Paste a color that you've copied
    • Pick a color from your QGIS app (activates a color dropper tool)
    • Open the Select Color pop-up (click "Choose Color...")

The copy and paste color functions are very useful if you are using the same colors across multiple layers, like if you're creating the same symbology for point, line, and polygon layers.

The Select Color pop-up can also be accessed by simply clicking the rectangle next to Color (instead of clicking the dropdown arrow and selecting "Choose Color...") and has even more functions...

  • On the top left side of the pop-up, you can choose between a color ramp, color wheel, color swatches, and color picker.
    • The color swatches have the option to switch between Recent colors, Standard colors, Project colors, and New layer colors.
  • On the right side of the pop-up, you can enter in HSV or RGB values, or type in values in HTML notation (you can switch between RRGGBB, RRGGBBAA, rgb, and rgba using the arrow dropdown). Selecting RRGGBB is useful for copying colors to paste over into ArcPro.

Rule Based Symbology

Rule-Based symbology provides even more freedom for class designations than you could achieve with either categorical or graduated symbology. It uses expressions that are very similar to SQL to define classes. A quick way to understand how QGIS rules are created is to change existing graduated or categorical symbology to rule-based (you could technically achieve all symbology goals by using rule-based symbology, but it's only necessary for more complicated scenarios). QGIS will automatically create corresponding rules for each class.

Creating rule-based symbology from scratch...

  1. Use the drop down at the top of the Symbology tab to select Rule-based.
  2. Use the green + button to add however many classes you need, and select any unneeded classes and use the red - button to remove them.
  3. Double click a class to open the "Edit Rule" pop-up.
    • Edit the text in the box next to Label to update the legend for that class.
    • Select the circle next to Filter (if it isn't already selected), and click the E (epsilson) button to open the Expression Builder pop-up, and set your expression
    • Edit your symbol, the same way you would in the Symbol Selector pop-up (see steps 6 and 7 in QGIS Symbology Basics)

Setting your expression

The left side of the Expression Builder pop-up is where you'll build your rule, the center section contains the function editor, and the right side provides information about whatever is selected in the function editor. Double click an item to add it to your expression building area.

You'll likely use items from these dropdowns for building your expression...

  • Fields and Values dropdown: Contains all the attribute field names and values for your layer.
  • Operators dropdown
  • Conditionals dropdown

General expression building tips

  • Field names are enclosed in quotes, for example: "Ownership" and "oCC_EX"
  • Text attribute values are enclosed in apostrophes, for example: 'State'
  • Numeric attribute values do not need to be enclosed in anything, for example: 5
  • If your expression is invalid, the "Preview:" area will let you know
  • Return to the "Edit Rule" pop-up and click Test to the right of E to see if your rule returns any features (keep in mind that a rule still may be valid if it returns no features, but if there are known features in your layer that should be picked up by that rule and aren't, then you know something is wrong with your rule)

Example Expressions

  • This expression returns objects where the Ownership attribute is State: "Ownership" = 'State'
  • This expression returns objects that have an existing dam capacity between 1 and 5, including 5: "oCC_EX" > 1 AND "oCC_EX" <= 5

Video Demonstrations

Creating and Testing .qml files

QGIS Symbology Basics

QGIS Rule-based Symbology

Page updated by Chloe Seeborg for USU's Riverscapes Assessment and Monitoring (RAM) Laboratory