# Monday Knowledge Snippet (MKS) – 32 As the crow flies (Air Line distance)

Just got the question what type of calculation SAP TM uses to determine distance / duration in case no GIS is connected to get real-street information. What in some scenarios might be sufficient, but in general we recommend for a better information quality to use such a tool. Especially when doing transportation planning.

But what is used when no GIS is available? SAP TM calculates the distance between the start and destination location using the master data coordinates taking the curvature of the earth into account. To come closer to reality, it is possible to define per means of transport a distance factor (in case not filled the system assumes a factor of 1). The calculated distance is multiplied with this factor. For example a means of transport for air might have a factor of 1 since it almost can fly like a crow, while of road you assume a deviation of 25 percent. Obviously this deviation is in reality different for different routes… But at least you are given the chance to adjust a bit here. Remember, in case you have a requirement to be very accurate here – use a GIS.

The duration between the start and destination location is calculated out of the above determined distance multiplied with the average speed maintained for the means of transport. The 3 other speeds you find there (low, medium, high) are used as input if a GIS is called.

Last setting here: You can tell the system per means of transport if you want the GIS to be called or not by checking ‘GIS Quality’. Since this is performance critical it should only be set if required.

The Air Line distance is always used in case no specific definition has been made. So in a system with no distance determination settings you should already see a distance between 2 location having diffferent coordinates without doing anything. More specific settings can be made under the customizing for the Transportation Lane.

An alternative for the distance determination somewhere inbetween Air Line distances and real GIS distances is to setup a DD stragegy and pre-fill the buffer from whatever source without having a GIS connected. This way you can use for unknown connections the Air-Line and for already known and maybe important routes more accurate values. System will pick up first the buffered values and for the rest apply the air line logic.

You can test the distance determination using report /SCMB/TEST_DDD.