Sort of MapServer related . . Stacked, or coincident points . . .

[Dylan Keon]

On 12/28/05, Bob Basques <bob.basques at ci.stpaul.mn.us> wrote:
> All,
>
> I need a way to handle a stacked point data set.  I'm working with a
> Address dataset that has some points that are stacked in the same spot.
> A few of them have hundreds of points in the same location, IE Apt.
> Buildings, etc.
>
> Has anyone worked with a similar dataset before from MapServer?
>
> We have some ideas about how to display the data.  Nothing concrete
> yet.  The current system relies on ImageMaps for the display of the
> point data via a MapServer Template.  This works for the first (last
> ImageMap record) in the imagemap, but how to view the other point
> records from the same point.   We're in the mode right now to build some
> Javascript handlers for a XML stream from MapServer, but this seems like
> overkill for some reason.
>
> The dataset is such that I can't seperate the different points very
> easily, nor should they I think.
>
> Any ideas out there?
>
> bobb


Hi Bob,

I once had a similar problem where I wanted to display an individual
point for each specimen collected from various research sites, where
each site was recorded as a single lat/lon.  Since so many specimens
shared the same coordinates, the points were often stacked.  The
options I considered were:

1) jitter the points by introducing a small amount of random error
into the coordinates (only works well when zoomed in pretty far).

2) plot a single point for each research site, with data for multiple
specimens contained in the attributes for that point.

3) render a single point of one color where multiple specimens were
collected at a site, and another color where a single specimen was
collected.

In my case option 2 worked out pretty well.  However, your data are
quite different and I wasn't doing imagemaps.  Also, my data were
selected and rendered dynamically based upon the user's query.  You
mentioned you can't separate the points easily - is your address
dataset stored in a database, or is it more static (shapefile)? 
Anyway, maybe this will give you some ideas.  HTH.

Dylan