Simple Things

PlacementA
spaced equidistantly
<circle cy="11" r=".5" stroke="black" stroke-width=".2" fill="yellow" >
    <replicate repeatCount="100">
        <replicateAttribute attributeName="cx" from="0" to="200"  />
    </replicate>
</circle>       
Equidistant spacing: replicate only; no randomness

PlacementB
Random uniform on x axis
<circle cy="31" r=".5" stroke="black" stroke-width=".2" fill="yellow" >
    <random attributeName="cx" min="0" max="200"  />
    <replicate repeatCount="100" />
</circle>
Uniformly distributed over the interval 0 to 200.

 PlacementC
normally distributes
<circle cy="51" r=".5" stroke="black" stroke-width=".2" fill="yellow" >
    <random attributeName="cx" min="0" max="200"  distribution="normal"/>
    <replicate repeatCount="100" />
</circle> 
Normally distributed    
      

Size
varying size of ellipses randomly under replication
<circle cy="11" r=".5" stroke="black" stroke-width=".2" fill="yellow" >
    <random attributeName="r" min="1" max="3"  />
    <replicate repeatCount="100">
        <replicateAttribute attributeName="cx" from="0" to="200"  />
    </replicate>
</circle>    
Varying the size of circles as they are replicated horizontally -- http://cs.sru.edu/~ddailey/svg/Size.svg


Color:
dots
    <random attributeName="fill"
      min="rgb(30, 45, 40)" max="rgb(160, 85, 40)" />
    <random attributeName="rx" values="12;26" />
Varying size/shape and color http://cs.sru.edu/~ddailey/svg/B0a.svg

Remark: RGB vs HSL (control vs browsers)
discrete vs continuous -- rx discrete; RGB continuous