add a typeahead box which selects the visible taxon
invoke a scope.$digest when the json data is assigned

else anything which should update when that changes, won't.
add a "loading" text, and a spinniung icon; make the text white with a shadow

This looks better and gives some feedback when the page is slow to load.
adjust styles to prevent the text shadow from fuzzing the drop-down text
add annotations to the circle markers

showing how many sigtings there are, what the gridref is, and how
recent the last one was.
utils.js - fix a bug in the tetrad suffix conversion
modify data format to be more compact, adjust algorithms/parsing accordingly
colour the circles by their age - green is newer, red is older.
www/js/tetrad-map.js - scale map to fit into screen

And to be zoomable using the g#scalar element.
www/js/tetrad-map.js - scale the svg to min x/y, not mid x/y
www/index.html - switch layout to have a fixed select box on the left

Instead of a typeahead drop-down
www/test-dataset.json - update to new data format
www/js/tetrad-map.js - add a date threshold paramter, with a two colour scheme

Newer than the date threshold, black.  Older, white.
csv2json.pl - now sorts the gridrefs by precision, to prevent eclipsing

Sort records by gridref precision, so that large circles are rendered
before small ones.  This means that the former don't eclipse the
latter.  Handily, a gridref's precision is related to its length in
characters (the longer the higher the precision)
www/cheshire-dataset.json - regenerate with sorted gridrefs
.gitignore perl local-lib in ll
www/js/tetrad-map.js - fix a bug in the scale calculation

One of the heights used in a pythagoras calculation is the wrong one,
thus giving an invalid result (NaN) - but only if the mapped points
differ in y coordinate (which has been the case so far).
www/basemap.jpg - update this, and the coords in index.html to match

This is a new map from Des Callaghan. "I attach a better basemap which
was produced at a scale  of 1:400,000. Coordinates of two corners are:
Bottom left: 317489,335687 Top right: 414432,406723"

I mapped Des' XY coords to gridrefs using http://gridreferencefinder.com/
csv2json.pl - discard records coarser than tetrad; convert rest to tetrads

Coarser gridrefs than tetrads cannot be attributed to the required
accuracy.  Finer than tetrad gridrefs need to be rounded up to the
enclosing tetrad.
cvs2json.pl - modify to use date:count hashes in taxon records

...instead of arrays of date.  Repitition of dates makes the latter
more verbose.