Input for arbitrarly large radius in map

Question

I'm developing a mobile app where the users need to select a point in a map, and then define a radius around this point. This will be used to define a Geofence and to perform an action when later the user enters this area.

At the moment, the user can select a point by touching the map, and then sets the radius using a seekbar. The circle drawn in the map updates dynamically with the changes in the seekbar.

My question is how to allow the user to input an arbitrarily large radius?

At the moment I have defined a maximum for the Geofence radius. But I would like to allow the user to define a radius as large as they want.

One idea would be to just increase the maximum of the seekbar when the user "pushes" the seekbar on the right edge. But then when pulling it back, the scale would feel weird: small changes in the seekbar are now huge changes in the radius.

Answer 1

I do not know the answer, But I would try 2 things:

1. Make the slider non-linear. Left corner 100m, right corner 40k km to cover the globe. Indicate left corner by walking figure. Right corner by the globe icon. Assumption is that people will need finer control near at smaller radius.

2. Get rid of slider and use zoom level to specify the radius. Make sure to indicate that current zoom level is actually meaningful by providing current radius value and the way to disable radius all together if applicable.

Answer 2

You could allow the user to enter a numeric value, perhaps under the guise of an "advanced" option or similar.

As @ErhanYaşar says, there will be a feasible max due to the fact the earth is a finite space and you need to trade of this against the level of precision the user needs to enter.

What is the purpose of the geofencing? what level of accuracy is required? what are the reasonable min and max?