On Mon, 26 Oct 2009 12:16:17 -0700
John Graybeal <graybeal at marinemetadata.org> wrote:
>Love the question! :->
>
>Are you saying every map location has one index value, which is one of the
>numbers from 1 to 827? So these are mutually exclusive? Or are there 827
>flag values assigned independently for each map location?
It sounds to me like it's the former case, and the problem is that
concatenating 827 flag values into a single string attribute makes
something that is easy for a machine to interpret, but impenetrable to
the human reader.
As I read section 3.5, there are no other options for encoding the
information according to spec; a gigantic flag_meanings attribute is
the right answer.
But if the issue is really usability, I think the answer is not to do
it differently, but just to add an extra attribute that presents the
same information in a more user-friendly format. You could add an
attribute named something descriptive, like "category_legend", and
pair the values & meanings up, one per line. Then you'd end up with
something that looks like this:
float landtype(yc, xc) ;
landtype:long_name ="Land cover type" ;
landtype:standard_name ="land_cover" ;
landtype:flag_values = 1.f, 2.f, 3.f, 4.f, 5.f, 6.f, 7.f, 8.f, 9.f,
10.f, 11.f, 12.f, 13.f, 14.f, 15.f, 16.f, 17.f, 18.f, 19.f, 20.f, 21.f, 22.f,
23.f, 24 .f;
landtype:flag_meanings ="Urban_and_Built-up_Land
Dryland_Cropland_and_Pasture Irrigated_Cropland_and_Pasture
Mixed_Dryland/Irrigated_Cropland_and_Pasture Cropland/Grassland_Mosaic
Cropland/Woodland_Mosaic Grassland Shrubland Mixed_Shrubland/Grassland Savanna
Deciduous_Broadleaf_Forest Deciduous_Needleleaf_Forest Evergreen_Broadleaf
Evergreen_Needleleaf Mixed_Forest Water_Bodies Herbaceous_Wetland
Wooden_Wetland Barren_or_Sparsely_Vegetated Herbaceous_Tundra Wooded_Tundra
Mixed_Tundra Bare_Ground_Tundra Snow_or_Ice" ;
landtype:category_legend ="\n",
"1: Urban and Built-up Land \n",
"2: Dryland Cropland and Pasture \n",
"3: Irrigated Cropland and Pasture \n",
"4: Mixed Dryland/Irrigated Cropland and Pasture \n",
"5: Cropland/Grassland Mosaic \n",
"6: Cropland/Woodland Mosaic \n",
"7: Grassland \n",
"8: Shrubland \n",
"9: Mixed Shrubland/Grassland \n",
"10: Savanna \n",
"11: Deciduous Broadleaf Forest \n",
"12: Deciduous Needleleaf Forest \n",
"13: Evergreen Broadleaf \n",
"14: Evergreen Needleleaf \n",
"15: Mixed Forest \n",
"16: Water Bodies \n",
"17: Herbaceous Wetland \n",
"18: Wooden Wetland \n",
"19: Barren or Sparsely Vegetated \n",
"20: Herbaceous Tundra \n",
"21: Wooded Tundra \n",
"22: Mixed Tundra \n",
"23: Bare Ground Tundra \n",
"24: Snow or Ice" ;
(Sorry for the length, but it gives a real sense of what I mean.)
The flag_values and flag_meanings attributes are still a mess to look
at, but they're easy to deal with programmatically, while end-users
can easily look at category_legend and figure out what cover type 22
is if that's all they're after.
Fundamentally, this is the same issue as the question of how to record
the grid mapping, and the underlying problem is that while attributes
allow you to associate key-value pairs with a variable, there's no way
to nest another associative array within an attribute; the best you
can do is reference a dummy container variable and look at *its*
attributes.
(Which is an approach that works well enough for the grid mapping
problem. It may be worth formalizing / regularizing it and applying it
to any attribute sets that are grouped together and have a tendency
toward being composed of long lists of elements...)
Cheers,
--Seth
----
Seth McGinnis
mcginnis at ucar.edu
NARCCAP Data Manager
IMAGe / ISP / NCAR
----
>On Oct 26, 2009, at 0710, <martin.juckes at stfc.ac.uk> wrote:
>
>> Hello,
>>
>> I wonder if anyone can help with this problem:
>>
>> I have a file with a map of index values, ranging from 1 to 827. The flag
>meanings range from ?Admiralty Islands lowland rain forests? to ?Zambezian
>halophytics?. I?m reluctant to combine all 827 flag meanings into a single
>string for the ?flag_meanings? attribute ? is there a better way?
>>
>> Note that this is not my dataset, so that while suggestions for presenting
>the data in a different way may be useful, they won?t solve my current
>problem. The dataset is a eco-region analysis distributed by the WWF and has
>wide usage in its present form.
>>
>> Sincerely,
>> Martin Juckes
>>
>> --
>> Scanned by iCritical.
Received on Mon Oct 26 2009 - 17:13:06 GMT
