Create and use a link map

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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.

The spread of an infectious disease

Create a link map

To create a link map, complete the following steps:

  1. Expand a dataset in the data pane so that the fields are visible.
  2. Select one of the following combinations of data:
    • Two location fields Location field
    • Two location fields Location field plus a number Number field or rate/ratio Rate/ratio field 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.

    You can search for fields using the search bar in the data pane.

  3. Drag the fields to the page and drop them on the Map drop zone.
    Note:

    You can also create a map by selecting a field and clicking the Map button above the data pane.

Usage notes

To access the Layer options pane, click the arrow next to the layer name. You can do the following in the Layer options pane:

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

SelectionSymbology SymbologyAppearance AppearanceLegend 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.

Use the Edge weight parameter to calculate weighted centrality values. By default, the Edge weight parameter is set to Uniform, meaning the centrality calculation is unweighted. You can choose a field to apply weights to the calculation. Edge weight is available for betweenness, closeness, and eigenvector centralities.

Use the Normalized parameter 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 you choose Natural Breaks or Equal Interval, you can also edit the number of classes.

Learn more about map classification

Use the Show pop-ups parameter to turn pop-ups off or configure pop-ups to display with or without statistics, like centrality values.

Click View centralities to create a reference table showing the centrality values for each node. The table includes a column for entity (field name), node (feature), and centrality.

Change the layer transparency of the link map.

Unavailable

Tip:

Drag-N Drop Drag a string field to the Layer options pane and drop it on the link to style the links by unique values.

Node

Use the Choose node field parameter to switch the selected node to a different location field.

Configure Node style options, including the following:

  • Symbol shape
  • Size (min - max)
  • Fill color
  • Outline thickness
  • Outline color

Unavailable

Use the Add button Add to page and Delete button Delete 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-N Drop 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. You can do the following:

  • Use the Merge nodes button Merge nodes and Unmerge nodes button Unmerge nodes to merge or unmerge the values from the From and To fields. Merging the fields sets the nodes to the same symbol.
  • Use the Unlink button Unlink and Link button Link to remove or add a link between two node fields. These options are only available if there are three or more node fields.

Link

Use the Weight parameter to change or remove the number or rate/ratio field being used to apply weight to the links.

Use the Type parameter to change or remove the string field being used to style the links by unique category.

Configure the Link style options parameter, including the following:

  • Pattern
  • Thickness (min - max)
  • Color

The Legend tab is enabled if a Weight field or Type field is added. The Legend tab can be used to view the classification values or unique categories for the links and to make selections on the chart.

If the arrows are pointing in the wrong direction, use the Flip button Flip to change the direction of the flow.

If the map includes three or more node fields, the Delete button Delete 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-N Drop Drag a number or rate/ratio field to the Layer options pane and drop it on the selected link to change the Weight parameter value. Use a string field to change the Type parameter value.

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

Use the Card filter button Card filter to remove any unwanted data from the card. Filters can be applied to all string, number, rate/ratio, and date/time fields. A card filter does not affect other cards using the same dataset.

Use the Selection tools button Selection tools to select features on the map using the single select, box select, and lasso tools; zoom to the selection; or invert the selection.

Use the Zoom tools button Zoom tools to zoom in or out on the map, zoom to a selection, set the default extent of the map, zoom to a layer, or lock navigation on the map.

The Visualization type button Visualization type 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 Display field set.

Use the Sync extents button Sync extents to link the extent of all maps on the page so they zoom and pan simultaneously.

Use the Maximize button Maximize to enlarge the card. Other cards on the page will be reduced to thumbnails. The card can be returned to its previous size using the Restore down button Restore down.

Use the Enable cross filters button Enable cross filters to allow filters to be created on the card using selections on other cards. Cross filters can be removed using the Disable cross filters button Disable cross filters.

Use the Flip card button Flip card to view the back of the card. The Card info tab Card info includes a count of features and a text box for a description of the card.

Use the Card options button Card options to access the following options:

  • Appearance button Appearance—Change the background color, foreground color, border of the card, and map rotation, and add or remove the basemap layers and north arrow.
  • Order button Order—Move the card forward or move the card backward relative to other cards on the page.
  • Delete button Delete—Remove the card from the page. If you did not intend to delete the card, you can retrieve it using the Undo button Undo.

Limitations

A limit to the number of connections that can be displayed is based on the maximum query limit for the dataset. The There's too much data to complete this operation error message is displayed if the number of connections is greater than the limit. The maximum query limit for point features is 16,000. The maximum query limit for line and area features is 8,000.

For example, a dataset of flights throughout Europe contains hundreds of thousands of flight numbers for 126 airports. Every airport has at least one direct flight to every other airport. Therefore, the number of connections is as follows:

126 origins * 126 destinations = 15876 connections

The number of flights does not affect the query limit, but the number of airports does. If one extra airport is added to the dataset with direct flights to all other airports, the number of connections increases to 16,129, which is over the query limit. However, if a connection does not exist between every unique value, the number of unique values can be higher. If some of the airports do not have direct flights between each other, the number of airports that can be displayed can increase until the number of connections surpasses the query limit.

Resources

Use the following resources to learn more about maps: