Insights for ArcGIS - Create and use a link map

Link maps are used in link analysis to show the relationships between locations. Link maps can show the relationships either without direction (spider lines) or with directions (flow maps). The connections can also show the magnitude of the relationship, such as the number of phone calls between locations.

Link maps help answer questions about your data, such as: How is it related?

Example

A nongovernmental health organization is studying the spread of an infectious disease during a past outbreak. A directed link map (also called a flow map) is used to visualize the spread from two of the countries hit the hardest by the disease to other countries.

Create a link map

To create a link map, complete the following steps:

Steps:

Expand a dataset in the data pane so that the fields are visible.
Select one of the following data options:
- Two location fields
- Two location fields plus a number or rate/ratio field
Tip:
One or more location fields can be added to your dataset using Enable Location or by creating a relationship with a dataset that has a location field. When enabling location for a link map by coordinates or addresses, it is best practice to keep the Repeat identical features parameter unchecked.
Drag the fields to the page and drop them on the Map drop zone.

Usage notes

Click the Info button Info to turn the map card over. The back of the card includes a place to write a description of the map.

The Layer options pane is accessible from the layer legend and can be used to change the style and statistics of the map.

Nodes can be sized using the following centrality methods:

Degree—The number of direct neighbors of the node. If the map is directed (a flow map), the degree can be measured as either indegree (the number of direct neighbors with connections directed toward the node) or outdegree (the number of direct neighbors with connections directed away from the node).
Betweenness—The extent to which a node lies on the shortest path between other nodes in the network. The normalization parameter is disabled for this centrality method because the betweenness calculation always applies normalization.
Closeness—The average of the shortest distance paths to all other nodes. The normalization parameter is disabled for this centrality method.
Eigenvector—The measure of the influence of a node in a network based on its proximity to other important nodes.

The Analysis tab and Style tab display different options based on the selections you make in the Layer options pane. The following options are available for link maps:


Selection	Options	Style	Legend
None	The Directional flow parameter can be used to change the links to arrows from one node to the other. The centrality method can be set from the Size node using parameter. The Normalized parameter can be used to normalize the node centralities by dividing by another field to create a ratio or proportion. The Normalized parameter is enabled by default but can be disabled for nodes using betweenness and closeness centrality. The Natural Breaks, Equal Interval, and Unclassed classifications can be chosen in the Classification type parameter. If Natural Breaks or Equal Interval is chosen, the number of classes can also be edited.	Change the layer transparency of the link map.	Unavailable
None	Tip: Drag a string field to the Layer options pane and drop it on the link to style the links by unique values.		Unavailable
Node	Use the Choose node field parameter to switch the selected node to a different location field.	Change the Node style options, including the following options: Symbol shape Size (min - max) Fill color Outline thickness Outline color	Unavailable
Node	Use the Add button and Delete button to add new node fields or delete existing node fields. New node fields will be connected to the selected node field. You must have three or more node fields to delete a node. Tip: Drag a location field to the Layer options pane and drop it on the Add button or on an existing node to add node fields. Use Ctrl+click to select multiple nodes. The following options are available: Use the Merge nodes button and Unmerge nodes button to merge or unmerge the values from the From and To fields. Merging the fields will set the nodes to the same symbol. Use the Unlink button and Link button to remove or add a link between two node fields. These options are only available if there are three or more node fields.		Unavailable
Link	The Weight parameter can be used to change or remove the number or rate/ratio field being used to apply weight to the links. The Type parameter can be used to change or remove the string field being used to style the links by unique category.	Change the Link style options parameter, including the following options: Pattern Thickness (min - max) Color	The Legend tab is enabled if a Weight field or Type field is added. The Legend can be used to view the classification values or unique categories for the links and to make selections on the chart.
Link	If the arrows are pointing in the wrong direction, use the Flip button to change the direction of the flow. If the map includes three or more node fields, the Delete button can be used to remove a link from the map. Deleting a link also removes a node field that has become disconnected from the rest of the map. Tip: Drag a number or rate/ratio field to the Layer options pane and drop it on the selected link to change the Weight parameter. Use a string field to change the Type parameter.

The distance between nodes can be viewed by hovering over the links. The distance is reported in the default units for your account.

The Visualization type button can be used to switch a link map to another visualization, such as a bar chart. To change the visualization type, the location fields must have a Display field set.

Limitations

A limit to the number of nodes that can be displayed is based on the maximum query limit for the dataset. The error message There's too much data to complete this operation will be displayed if the number of nodes is greater than the limit. You can check the maximum query limit for a layer using the MaxRecordCount in the ArcGIS REST Services Directory.