Recently, I had to implement an offline mapping solution for an iOS application. Here's a walkthrough of how to do it.
|/* HC-SR04 Sensor|
|This sketch reads a HC-SR04 ultrasonic rangefinder and returns the|
|distance to the closest object in range. To do this, it sends a pulse|
|to the sensor to initiate a reading, then listens for a pulse|
|to return. The length of the returning pulse is proportional to|
|the distance of the object from the sensor.|