GIS Question of the Day #5 - Symbology

Question:

In ArcGIS, Is Symbology displayed on map/layer using database column or external link or something else?

Answer:

In ArcGIS, symbology is typically determined by the attributes stored in the database columns of your dataset. Here’s how symbology is applied and managed:

Symbology Sources in ArcGIS

1. Database Columns (Attributes):

   • Attribute-Based Symbology: Symbology is often based on the attribute values in your dataset. For example, different colors, sizes, or symbols might be used to represent different categories, ranges, or specific values in an attribute column.

   • Dynamic Updates: Changes in attribute values can dynamically update the symbology if the symbology is set to reflect those values.

2. Symbology Definitions:

   • Styles and Symbols: ArcGIS includes built-in styles and symbol sets that can be applied to layers. These predefined styles can be customized and applied based on attribute values.

   • Custom Symbols: Users can create and import custom symbols (such as PNG or SVG files) and apply them based on attribute values or other criteria.

3. External Links (Referenced Images):

   • URL-Based Symbology: In some cases, symbology can be defined using external links. For example, image URLs can be used to symbolize points with specific icons hosted externally.

   • Dynamic Web Maps: Web maps in ArcGIS Online or ArcGIS Enterprise can reference external images for symbols, allowing for dynamic updates without changing the underlying data.

Implementing Symbology Based on Database Columns

1. Attribute Table:

   • Ensure your dataset’s attribute table includes the necessary columns for defining symbology. For instance, if you are symbolizing by category, make sure there is a column that categorizes your data appropriately.

2. Setting Symbology in ArcGIS Pro:

   • Open Symbology Pane: Right-click the layer in the Table of Contents and select “Symbology.”

   • Choose Symbology Type: Select the appropriate symbology type (e.g., Single Symbol, Graduated Colors, Unique Values).

   • Assign Attributes: Set the attribute field(s) that will determine the symbology. Customize the appearance based on the attribute values.

3. Web Maps and Dashboards:

   • When creating web maps or dashboards in ArcGIS Online or ArcGIS Enterprise, configure the symbology in the web map settings. Attribute-based symbology can be set similarly to how it’s done in ArcGIS Pro.

Example: Symbology Based on Attribute Values

1. Categorical Symbology:

   • Unique Values: Use unique value symbology to assign different colors or symbols to different categories based on an attribute field (e.g., land use types, zoning categories).

2. Quantitative Symbology:

   • Graduated Colors: Use graduated color symbology to represent numerical ranges (e.g., population density, elevation).

   • Proportional Symbols: Use proportional or graduated symbol symbology to represent numerical values with varying symbol sizes.

3. Custom Symbols:

   • Import custom symbols (PNG, SVG) and apply them based on attribute values or conditions.

Summary

Symbology in ArcGIS is primarily driven by the attribute data stored in the database columns of your layers. This attribute-based symbology allows for dynamic, data-driven visualization. Additionally, external links or referenced images can be used for more customized or dynamic symbology needs, especially in web maps and applications.

By leveraging the power of attribute-based symbology and customizing it with styles and external resources, you can create highly informative and visually appealing maps in ArcGIS.