iPhone : MapKit and displaying the current Map Scale

I need to display on the map a scale showing how far a inch / cm is for example. This will need to change depending on the zoom level.

My theory is that if I know the length of the map, and the length of the graphic, If I know what the current scale of the map was I could just do some maths to work out the graphic indicator scale.

So is there 开发者_开发问答a way to get the current zoom lvl in meters? Is it linked to the span or something?

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The zoom level is linked to the span - you first need to get the span of your map view, and then convert it into meters.