Preface The mobile phone, and specifically the iPhone which continues to define the state of the art for smart phones, has become the primary interface device for geographically tagged data. More recently the ability to overlay data layers on a real time camera view, a technology that has been the stuff of science fiction for some years, means that this geographically tagged data has left the map and "flatland" behind. The killer app for the iPhone may yet well prove to be geo-location Augmented Reality. This book is (mostly) about that. Who Should Read this Book? This book provides an introduction to the hot topic of location-enabled sensors on the iPhone. If you are a programmer who has had some experience with the iPhone before, this book will help you push your knowledge further. If you are an experienced Mac programmer, already familiar with Objective-C as a language, this book will give you an introduction to the hardware specific parts of iPhone programming. What You Should Already Know? The book assumes some previous experience with the Objective-C language. Additionally some