Why do we need to specific size during vector image generation in Android Studio?

Question

I first thought the purpose of Vector assets is that, it enables us to scale up/ scale down without compromise image quality.

If so, may I know why do we need to specific size during vector image generation in Android Studio?

I tend to generate 2 different sizes of Vector.

24x24

<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="24dp"
    android:height="24dp"
    android:viewportHeight="24.0"
    android:viewportWidth="24.0">
    <path
        android:fillColor="#FF000000"
        android:pathData="M19,2h-4.18C14.4,0.84 13.3,0 12,0c-1.3,0 -2.4,0.84 -2.82,2L5,2c-1.1,0 -2,0.9 -2,2v16c0,1.1 0.9,2 2,2h14c1.1,0 2,-0.9 2,-2L21,4c0,-1.1 -0.9,-2 -2,-2zM12,2c0.55,0 1,0.45 1,1s-0.45,1 -1,1 -1,-0.45 -1,-1 0.45,-1 1,-1zM19,20L5,20L5,4h2v3h10L17,4h2v16z"/>
</vector>

96x96

<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="96dp"
    android:height="96dp"
    android:viewportHeight="24.0"
    android:viewportWidth="24.0">
    <path
        android:fillColor="#FF000000"
        android:pathData="M19,2h-4.18C14.4,0.84 13.3,0 12,0c-1.3,0 -2.4,0.84 -2.82,2L5,2c-1.1,0 -2,0.9 -2,2v16c0,1.1 0.9,2 2,2h14c1.1,0 2,-0.9 2,-2L21,4c0,-1.1 -0.9,-2 -2,-2zM12,2c0.55,0 1,0.45 1,1s-0.45,1 -1,1 -1,-0.45 -1,-1 0.45,-1 1,-1zM19,20L5,20L5,4h2v3h10L17,4h2v16z"/>
</vector>

The content looks same except for android:width and android:height parameters.

Answer 1

I can't give you a full explaination, but here is what I think.

Some image containers really depend on the size of the drawable to draw the image correctly. They cannot use viewportHeight and viewportWidth, so width and height is what they look for.

In my case, when loading a Marker on GoogleMap, I cannot change the size of marker programatically. The map use the exact size of the drawable to be the size of the marker. When I use VectorDrawable for the marker, I have to modify the width and height to the marker size I want.

The GoogleMap Marker is the image container I am talking about that always need the exact source's size.