Flow, process and networks
Flow / origin-destination map
Connects origins to destinations and optionally sizes links by flow magnitude.
- Map
- Flow
- Geography
What it answers
Where do flows originate and end?
- Shape
- Locations linked by lines or arcs
- What it shows
- Main corridors and directional imbalance.
Example
The question
How many shipments go from the central warehouse to each city?
Weekly shipments from the central warehouse (flow map)
Illustrative data. It belongs to no company.
When to use it
Use it when
Geographic transfers and movement summaries.
Avoid it when
When connectors are mistaken for actual travel routes.
How to read it
Follow direction fromorigin todestination and compare widths if encoded.
Note
Connectors need not follow actual routes.
The data you need
- Layout
- Two linked tables
- Fields
- SourceID,TargetID: text; Value: number; endpoint coordinates in a separate locations table
- One row is
- One geographic origin-to-destination flow. What is the grain?
- Rules
- Both endpoints must resolve to valid geographic locations. Define flow direction and units.
- Optional
- Alternative: SourceLon,SourceLat,TargetLon,TargetLat,Value.
- Preparation
- Resolve node identities and endpoint joins; define direction and duplicate/self-link handling. Aggregate weights only under a stated relationship or flow definition.
- Units
- Unweighted links encode presence. Weights need a unit; flow shares divide by stated source, destination or network totals, not an assumed common denominator.
Worked example
A->B30, B->A10. Draw separately directed links. Netflow is 20 from A to B under this unit definition.
| Links: SourceID | TargetID | Value |
|---|---|---|
| A | B | 30 |
| Locations: ID | Longitude | Latitude |
| A | 18.07 | 59.33 |
| B | 11.97 | 57.71 |