Arecibo mapping is reported of the neutral hydrogen distribution along selected directions out from the centers of two examples of small High Velocity Clouds ( HVC ) .
One HVC ( W486 ) is selected from the class of Compact HVCs ( CHVCs ) thought by some researchers to be good candidates for having distances characteristic of the Local Group ; the other ( W491 ) is a bit more extended and possibly nearer .
Both HVCs have a small inner region where the neutral hydrogen column density N _ { HI } decreases slowly and a larger outer region where N _ { HI } declines more rapidly , smoothly and exponentially from \sim 2 \times 10 ^ { 19 } { atoms } { cm } ^ { -2 } down to < 10 ^ { 18 } { atoms } { cm } ^ { -2 } .
Line widths , and presumably temperature and turbulence , do not increase in the outermost regions .
Therefore pressure decreases smoothly , making confinement by dark matter gravity more likely than confinement by external pressure .

The more extended HVC , W491 , has a superimposed small cloud ( which we dub a “ mini-HVC ” ) , offset by 66 { km } { s } ^ { -1 } in velocity along the line of sight .
The peak column density of the mini-HVC is about 5 \times 10 ^ { 18 } { atoms } { cm } ^ { -2 } .
Preliminary data toward future mapping of two more HVCs reveals two more mini-HVCs of similarly small size and central column density a bit less than 1 \times 10 ^ { 19 } { atoms } { cm } ^ { -2 } , offset by an even larger velocity , \sim 98 { km } { s } ^ { -1 } .
We suggest that these three mini-HVCs are not physically associated with the HVCs on which they are superimposed , but are either very small outlyers of the extended Magellanic Stream HVC complex or more distant and/or smaller isolated CHVCs .

The importance of the edge column density N _ { 1 / 2 } , the value of N _ { HI } at the point where the neutral and ionized column densities are equal , is discussed .
With N _ { 1 / 2 } \sim 2 \times 10 ^ { 19 } { atoms } { cm } ^ { -2 } for the two mapped HVCs , the angular scalelength of the total hydrogen is appreciably larger than the observed H i scalelength .
Previous distance estimates , related to absolute size and mass of the total hydrogen cloud , may have to be scaled down because of the undetected , more extended ionized hydrogen .