原文链接：http://developer.android.com/tools/help/vector-asset-studio.html
概要：
（1）Compared to raster images, vector drawables can reduce the size of your app and be resized without loss of image quality. They help you to more easily support different Android devices with varying screen sizes and resolutions because you can display one vector drawable on all of them.
（2）one XML file that describes the image. Maintaining one XML file can be easier than updating multiple raster graphics at various resolutions.
https://design.google.com/icons/
（4）The initial loading of a vector graphic can cost more CPU cycles than the corresponding raster image. Afterward, memory use and performance are similar between the two. We recommend that you limit a vector image to a maximum of 200 x 200 dp; otherwise, it can take too long to draw.
（5）Only Android 5.0 (API level 21) and higher supports dynamic attributes
（6）When your minimum API level includes Android 4.4 (API level 20) or lower, you have corresponding vector and raster images in your project. In this case, you have two options for delivering your APK files:
Create one APK that includes both the vector images and the corresponding raster representations. This solution is the simplest to implement.
Create separate APKs for different API levels. When you don’t include the corresponding raster images in the APK for Android 5.0 (API level 21) and higher, the APK can be much smaller in size. For more information, seeMultiple APK Support.
