The space occupied by Apps and App Data can be found out using the options available as part of the settings screen on Google Nexus 7. Listed below are the steps with screens shots to find out the storage space taken by the apps.
Step 1: Tap the icon list and then the Settings icon on Google Nexus Home screen.
Step 2: In the Settings screen, tap the Apps option under Device section.
Step 3: The Apps screen will display the list of apps installed and the space occupied by each app. Also at the bottom of the screen you will find the free and used internal storage space.
Step 4: By tapping on the app, you can also find out the storage space taken by the app installation files and user data.
If you are not using the app and want to free up space then tap the Uninstall button. If you just want to clear only the app data then tap the Clear data button.