Shape Drawable Size not working

For me, setting the gravity of the item to "center" solved the issue. For example:

<item android:id="@android:id/progress" android:gravity="center">
    <clip>
        <shape>
            <size android:height="2dp"/>
            <solid android:color="@color/my_color"/>
        </shape>
    </clip>
</item>

It can work with a foreground. It seems like you can't set a background's gravity. But you can on a foreground. I checked API 21, 23 and 24 (well, with the Studio design preview) and the following places a solid circle dot on the ImageView.

<shape android:shape="oval" xmlns:android="http://schemas.android.com/apk/res/android">
    <solid android:color="@color/colorPrimary" />
    <size android:height="8dp" android:width="8dp" />
</shape>

With the layout snippet

    <ImageView
            android:foreground="@drawable/list_new_dot"
            android:foregroundGravity="right|center_vertical"
            tools:src="@drawable/model_1_sm"
            />

UPDATE: While it appears to work in the layout design tool, it doesn't look the same in the emulator. UPDATE 2: Since this answer has a few votes, you might want to check what I actually used in order to show a new indicator dot: https://gist.github.com/CapnSpellcheck/4d4638aefd085c703b9d990a21ddc1eb

Just to specify the user983447's answer - the size attribute does really mean a proportion. You should set the size for all shapes in your layer-list and it'll be used a as a proportion when scaling - like the layout_weight attribute of LinearLayout. So it's better to name it not a size but a weight

Below is a work-around how to implement top and bottom white lines without using the size attribute:

<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape>
            <solid android:color="#fff" />
        </shape>
    </item>
    <item android:top="1dp" android:bottom="1dp">
        <shape>
            <solid android:color="#888" />
        </shape>
    </item>
</layer-list>

I found the layer-list to be very devious for a first time Androider because of the following. At first glance most would think item top,bottom,right,left attributes are FROM the top,bottom,right,left. Where a value of the following:

<item android:top="10dp">

Would net you a starting point 10dp from the top of the respective container. This is not the case. Think of it as OFF OF the top,bottom,right,left. <item android:top="10dp"> will still net you a starting point 10dp OFF OF the top, but what happens when you want to set the bottom?

<item android:bottom="20dp">

This will not get you a bottom at 20dp from the TOP, rather a bottom of 20dp OFF OF the BOTTOM of the container.

So, for example with a 100dp container, if you wanted a rectangle with a top edge starting at 20dp and a bottom edge at 40dp:

<item android:top="20" android:bottom="60dp">