There are some reasons due to which a Google map is not displayed in Android Application instead a grey portion with squares is displayed. Some possible reasons are as follows.
Do not using API key : In order a Google Map to be displayed on your application, you need a unique API key. You need to set it in the constructor of the MapView or using the attribute android:apiKey if you are constructing a MapView from an xml layout. If you do not use API key, Google map will not display.
If API key is wrong: You need to specify the Google maps key that is generated for the keystore you are signing your application with. If you supply other API key that is not generated for the keystore that you sign you application with, no map will be displayed.
If you don’t have internet permission: Google map needs an internet connection. If your android OS doesn’t give the permission for internet, then the map will not display. To request an internet permission, add the following tag on AndroidManifest.xml file outside <application></application>.
<uses-permission android:name="android.permission.INTERNET" />
If you don’t include map library: This may be the another reason for the problem. Use the add the Google map library inside <application></application> as below
<uses-library android:name="com.google.android.maps" />