Working with various views inside your layout file to create a UI isn't always as straightforward as you want it to be. The Hierarchy Viewer, located in the Android SDK tools directory, lets you see exactly how your widgets are laid out on the screen in a graphical representation. This format allows you to clearly see each widget's boundaries so that you can determine what's going on inside your layout. This is the ultimate tool to make pixel-perfect UIs. The Hierarchy Viewer also lets you magnify the display in the pixel-perfect view to make sure that your images and UIs will display flawlessly on all screen sizes and densities. You can read all about it at http://developer.android.com/guide/developing/tools/hierarchy-viewer.html.