Your data
What goes in each field well, how the rows you give become flows on the map, and where the limits are.
The field wells
| Well | Takes | What it does |
|---|---|---|
| Origin | Place name | Required. Where each flow leaves from: a country, city or port name, or an ISO code. |
| Destination | Place name | Required. Where each flow arrives. |
| Value | Measure | Sets the thickness of each flow, in every view. Without it, each distinct combination of the fields counts as one. |
| Objective | Measure | Enables the Variance to objective view Premium. |
| Previous value | Measure | Enables the What changed view Premium: appeared, gone, up, down or stable. |
| Category | Column | Colours the flows in the Value view - a transport mode, a carrier, a product line. |
| Tooltips | Measures | Extra figures shown in the hover and click cards of each flow. When several rows make one flow, the figure comes from the first of them and is not added up (in Net it shows -). As many as you like. |
| Origin latitude, Origin longitude, Destination latitude, Destination longitude | Column | Optional. Exact coordinates. When they are given, they place the point; the name is only used as a label. |
| Origin country, Destination country | Column | Optional. Your existing country column - or a US state, Canadian province, UK nation or Australian state - to tell apart places that share a name: Toledo in Spain or in Ohio. No need to merge it into the name. |
| Origin display name, Destination display name | Column | Optional. The label to show. It is never used to locate the place: keep a technical code in Origin and put the readable name here. |
| Extra measures (max 2) | Measures | Each one adds a view Premium, named after it, in which that measure sets the colour. Thickness stays the Value. |
| Extra categories (max 2) | Columns | Each one adds a view Premium in which colour follows that column. |
How rows become flows
Every row whose origin and destination can be placed is part of a flow. Rows with the same origin and the same destination are added together into one arc: their values, objectives and previous values are summed. At country or continent level, all the cities of a country merge the same way. The Diagnostics panel counts how many rows were merged at the current level.
- A row from a place to itself draws no arc; its value counts in that place's activity, shown as Internal in the place card. The same goes, at country or continent level, for a row whose two ends fall in the same country or continent - the Diagnostics panel counts them.
- A row with no origin or no destination is left out, and a notice says how many.
- A Value that is not a number - the result of a division by zero, for instance - is counted as 0, and a notice names the rows.
- An objective present on only some rows of a flow is not used for that flow: it is treated as having no objective, and the card says Partial - not used.
Two directions between the same places
When two places send flows to each other, Reciprocal flows in Options chooses between Split, which draws both arcs, and Net, which draws one arc for the balance. In Net the thickness is that balance; the legend says Net next to the Value, and the card of the arc gives each direction's own total. Net needs a Value measure: without one, the setting is greyed. See Map and cards.
Measures that should not be added up
The visual receives what Power BI aggregates, then adds up the Value of every row that falls into the same flow - across categories, coordinates, and all the cities of a country at country level. A stock level, a rate or an average cannot be added up: keep an additive measure in Value. A rate belongs in Extra measures, where the Measure type setting averages it, weighted by Value - see The views.
A previous value, in DAX
The Previous value well takes a measure, usually the same measure over an earlier period. With a date table marked as such, last year's value for the same filters is:
Previous value = CALCULATE ( [Value], SAMEPERIODLASTYEAR ( 'Date'[Date] ) )
Any period works - last month, last quarter, a budget version - as long as it is a measure. The report's own date slicer then sets both periods at once.
Limits
- Rows. Power BI limits how many rows it sends to a visual. A row is one combination of every column placed in the wells - Origin, Destination, Category, coordinates, country and display-name columns, extra categories. Each column you add can multiply the rows, so keep only the ones you use. The visual asks Power BI for further batches, up to 200,000 rows; if Power BI still has rows to send beyond that, a Row cap reached notice says so. If the host declines to send more, the visual cannot tell.
- Flows drawn. By default the 2,000 largest flows are drawn. The Render limit in the Format pane goes up to 5,000; beyond it, a notice says how many flows were left out, and the largest are always the ones kept.
- Extra fields. Two extra measures and two extra categories at most.