Three measurements, three purposes
Distance has a different meaning in the airport map and the ground-cost comparison. Use the right measurement for the question you are answering.
Straight-line airport distance
Calculated from two airport coordinates. It is useful for choosing a geographic search area, not following a road.
Assumed budget distance
A geographic distance multiplied by an editable factor. It gives a transparent starting assumption for a budget, not evidence that a route exists.
Entered road distance
Mileage you supply after checking an actual drivable route. It replaces the automatic mileage assumption in the comparison, but does not turn an estimated driving time into a live traffic prediction.
Where the radius starts
The planner’s radius is centered on your selected home airport, not your home address or device location. Changing that airport changes the center of the circle and the alternatives inside it.
The map shows eligible airport locations. It does not establish airline coverage, a route to your destination or a currently available fare. Expanding the circle broadens the geographic shortlist; it does not guarantee a lower price.
A transparent assumption, not directions
For eligible automatic comparisons, the initial budget uses 1.25 times straight-line mileage and an assumed average speed of 55 MPH. Both values are assumptions that can be adjusted.
For illustration, 100 straight-line miles × 1.25 gives 125 budget miles. At an assumed 55 MPH, that is roughly 2 hours 16 minutes before adding any airport waiting time. This example is not a real airport route or a predicted arrival time.
Road layouts, bridges, traffic and access restrictions are not inferred from the circle. The model also does not infer ferry availability or whether a trip is practical by road. Automatic mileage assumptions are withheld for Alaska/Hawaii comparisons, specified island airports and airport pairs more than 500 straight-line miles apart; a confirmed drivable distance is needed instead.
A budgeting assumption is not a routing service. Do not use an estimated distance or time as directions or a promised arrival time.
Replace the assumption carefully
When using the airport-comparison controls, check directions between the selected home airport and the alternative airport, then enter that airport-to-airport road mileage. If the return route differs, record its distance separately where available.
An entered distance does not establish the travel time. When you have not entered a time, the model can still use the assumed average speed. Check your actual departure conditions independently and allow separately for terminal access, check-in, security and your own buffer.
For a complete real-world journey, also compare routes from your actual starting point to each airport. Travel from your house to the selected home-airport reference is excluded from the app’s added-driving calculation.
What to do when the route is unclear
Leave the distance unresolved rather than treating missing mileage as zero. First establish whether the route is usable for your vehicle and travel date. Then build the ground-cost budget from the verified route and clearly labeled assumptions.
You can use the airport map to explore options without claiming that any one of them is cheaper, quicker or easier for you.