[SDI-Africa] National level QDGC files for Africa

Tue Oct 30 21:06:05 EDT 2007

This is an announcement of the availability of Quarter Degree Grid Cells 
(QDGC) on a national level for African countries. The files are 
available on this website:

    * www.qdgc.org <http://www.qdgc.org/>

This announcement has been sent to the mailing lists of "SDI-Africa", 
"Society of Conservation and GIS" and the "Tanzania GIS User Group".

QDGC (or QDS - Quarter degree Squares) are a way of dividing the 
longitude latitude degree square cells into smaller squares, forming in 
effect a system of geocodes. QDGC represents a way of making (almost) 
equal area squares covering a specific area to represent specific 
qualities of the area covered. The squares themselves are based on the 
degree squares covering the Earth.

QDGC is currently used as a geocoding system for atlases. It has been 
used quite a lot on the African continent as the suitability is best 
between +40/-40 latitude degrees of the Equator. Examples are “/The 
atlas of southern African birds”/ by Harrison et al (1997), Tanzania 
Bird Atlas (www.tanzaniabirdatlas.com) and Tanzania Mammal Atlas 
(www.tanzaniamammals.org) to have mentioned some.

The initial QDGC standard as used by Harrison et al (1997) had some 
shortcomings, and was subsequently updated. For more information on this 
work see the references listed in the end of this email.

Together with T.Holmern, H. Maliti and E. Røskaft, I am working on a 
paper for a more detailed presentation of this work. Should anyone have 
a suggestion for an appropriate journal to publish such a paper we are 
open for suggestions.

The presented files are a work in progress. I would particularly welcome 
suggestions to adjusted attributes and meta-data associated with the 
files. For references use the QDGC website until further notice. The 
full set will be associated with the afore mentioned paper.

- - - - -

Last update of the QDGC files were made in January earlier this year 
(2007). Improvements were made based on these pending issues:

    * slightly inaccurate center points
    * no corner coordinates
    * separate files for separate countries
    * inadequate file nomenclature

This has now been fixed for QDGC level 1 and 2.

The users should note that the only squares exported for each country 
file are those in part or completely overlapping with the country shape 
file (the technical term is "intersect"). Some of the squares 
intersecting the border would thus not be completely within the related 
country's border and thus shared with the neighboring country.

A list of the new files are available on these pages at www.qdgc.org 
<http://www.qdgc.org>:

    * QDGC Level 1 overview page
      <http://www.qdgc.org/tikiwiki/tiki-index.php?page=qdgc_01>
    * QDGC Level 2 overview page
      <http://www.qdgc.org/tikiwiki/tiki-index.php?page=qdgc_02>

Browsing in the file repository is available here:

    * qdgc_01 file repository
      <http://www.qdgc.org/tikiwiki/tiki-list_file_gallery.php?galleryId=5>
    * qdgc_02 file repository
      <http://www.qdgc.org/tikiwiki/tiki-list_file_gallery.php?galleryId=6>

To facilitate the identification of the squares and ease the use of them 
in different contexts several attributes are provided with the files:

**

*Atribute***

*Description*

*ARAEA*

Calculated with XTools Km2, projected Coordinate System type, Albers 
Equal-Area? 
<http://tzgisug.or.tz/tikiwiki/tiki-editpage.php?page=Equal-Area> Conic 
Projection (ref: ArcGIS and Wikipedia 
http://en.wikipedia.org/wiki/Albers_projection) 
<http://en.wikipedia.org/wiki/Albers_projection%29>

*QDGC*

QDGCc string eg S01E003A? 
<http://tzgisug.or.tz/tikiwiki/tiki-editpage.php?page=S01E003A>

*LON_C*

Square centerpoint longitude calculated With XTools

*LAT_C*

Square centerpoint latitude calculated With XTools

*LON_NW*

Square north-western longitude

*LAT_NW*

Square north-western latitude

*LON_NE*

Square north-eastern longitude

*LAT_NE*

Square north-eastern latitude

*LON_SE*

Square south-eastern longitude

*LAT_SE*

Square south-eastern latitude

*LON_SW*

Square south-western longitude

*LAT_SW*

Square south-western latitude

<http://tzgisug.or.tz/tikiwiki/tiki-browse_image.php?imageId=69>QDGC 
shapefiles for the African continent. A work in progress.

/Figure: QDGC shapefiles level 2 reference E030S10CB../

More information and links to the different national files are available 
from the QDGC website://

    * http://www.qdgc.org

- - - - -

Further work based on the QDGC is being planned:

    * Steven D. Prager with the University of Wyoming has helped me with
      a script to speed up the process of generating later QDGC updates.
      Minor edits to the scripts will be made.
    * Prepare files for QDGC levels 3-5 for each country.
    * Update the QDGC website adding the lonlat2qdgc tool (python script).
    * Remove QDGC related files from the TZGISUG website
    * Make a .kml/kmz file based on the shape files.
    * Do the last 3-5 days of work on the paper and submit it to a
      journal to document what has been done.
    * I am looking into the possibilities of integrating the QDGC files
      in an African continent stand-alone atlas system using HostGIS,
      MySQL and PHP. This could prove to be a useful tool for baseline
      biodiversity studies.
    * I have set up a CVS (version repository) for my own use on a
      server. There is a possibility I might open it for anonymous read
      access.
    * Check if other countries around the Equator could find this
      geocoding standard useful.

            - - - - -

The work done on the QDGC files so far has not been explicitly funded. 
As such it has relied on me being able to do this on my spare time. 
_Should anyone feel that this work deserves some funding then just send 
me an email for more details_.

Money is not everything, and the work work so far would not have been 
possible without the skillful help from officers at the Tanzania 
Wildlife Research Institute, Dept of Biology at Norwegian University of 
Technology and Science, Tanzania Mammal Atlas Project, Tanzania Bird 
Atlas, Julian Blanc, Howard Frederick, Grant Hopcraft and a lot more. 
The Avian Demography Unit at University of Cape Town deserves a special 
mention for being the first ones to actually document the use of  QDGC/QDS.

Again - should you have any comments, questions or advice related to my 
work on QDGC please send me an email.

Regards,

Ragnvald Larsen

Harrison JA, Allan DG, Underhill LG, Herremans, M, Tree AJ, Parker V, 
Brown CJ (eds) 1997. The atlas of southern African birds. Vol. 1: 
Non-passerines. Vol. 2: Passerines. Johannesburg: BirdLife South Africa.

Larsen, R. 2006. Web mapping biodiversity. Website article at Tanzania 
GIS User Group website (http://tzgisug.or.tz).

Larsen, R. 2006. Bridging data repositories - introducing 
lonlat2qdgc.exe. Website article at Tanzania GIS User Group website 
(http://tzgisug.or.tz).

Larsen, R. 2006. Generating QDGC files (Updating QDGC revisited). 
Website article at Tanzania GIS User Group website (http://tzgisug.or.tz).

Larsen, R., Mduma, S., Maliti, H., Kaaya, J., Machoke, M. and Frederick, 
H. 2005. Generalisation of spatial wildlife data in Tanzania. Arusha. 
TAWIRI conference.

Wikipedia. http://en.wikipedia.org/wiki/QDGC

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