Example
SVG Patterns behave significantly differently than CSS background images when filling equivalent shapes. This can lead to significant surprises for new-comers to SVG. Below are examples of a pattern defined in all possible combinations of patternUnits and patternContentUnits - showing how these settings affect fill behavior.
<svg width="800px" height="800px">
<defs>
<pattern id="pattern1" x="0" y="0" width="0.2" height="0.2" patternUnits="objectBoundingBox" patternContentUnits="userSpaceOnUse">
<circle cx="10" cy="10" r="10" fill="blue" />
</pattern>
<pattern id="pattern2" x="10" y="10" width="20" height="20" patternUnits="userSpaceOnUse" patternContentUnits="objectBoundingBox">
<circle cx=".1" cy=".1" r="0.1" fill="blue" />
</pattern>
<pattern id="pattern3" x="10" y="10" width="20" height="20" patternUnits="userSpaceOnUse" patternContentUnits="userSpaceOnUse">
<circle cx="10" cy="10" r="10" fill="blue" />
</pattern>
<pattern id="pattern4" x="0" y="0" width="0.2" height="0.2" patternUnits="objectBoundingBox" patternContentUnits="objectBoundingBox">
<circle cx=".1" cy=".1" r="0.1" fill="blue" />
</pattern>
</defs>
<rect x="10" y="10" width="100" height="100" stroke="black" fill="url(#pattern1)"/>
<rect x="150" y="10" width="200" height="150" stroke="black" fill="url(#pattern1)"/>
<text x="10" y="200">patternUnits="objectBoundingBox" (20% of shape)</text>
<text x="10" y="220">patternContentUnits="userSpaceOnUse" (20px circle) </text>
<text x="10" y="240" stroke="blue" stroke-width="1">(Units used by default)</text>
<rect x="10" y="310" width="100" height="100" stroke="black" fill="url(#pattern3)"/>
<rect x="150" y="310" width="200" height="150" stroke="black" fill="url(#pattern3)"/>
<text x="10" y="500">patternUnits="userSpaceOnUse" (10px square box)</text>
<text x="10" y="520">patternContentUnits="userSpaceOnUse" (20px circle) </text>
<rect x="410" y="10" width="100" height="100" stroke="black" fill="url(#pattern2)"/>
<rect x="550" y="10" width="200" height="150" stroke="black" fill="url(#pattern2)"/>
<text x="410" y="200">patternUnits="userSpaceOnUse" (10px square box)</text>
<text x="410" y="220">patternContentUnits="objectBoundingBox"(radius="10%") </text>
<rect x="410" y="310" width="100" height="100" stroke="black" fill="url(#pattern4)"/>
<rect x="550" y="310" width="200" height="150" stroke="black" fill="url(#pattern4)"/>
<text x="410" y="500">patternUnits="objectBoundingBox" (20% of shape)</text>
<text x="410" y="520">patternContentUnits="objectBoundingBox"(radius="10%") </text>
</svg>
