[TZGISUG] Tanzania Polygon

[Mike Shand]

Hi Howard,

The Download zip file from NBS has 4 shapefiles - region; district; 
international bdy; and *water body*.

My observations on the shapefiles are that:
(a) The Water Body and the Districts shapefiles fit to each other.
(b) The Regions and the International Boundary shapefiles fit to each other.
There is a 250-300m shift between (a) and (b).
It does not appear to be a simple projection shift.
This then poses the question - which pair of shapefiles are correct - I 
have overlaid them all on Google and OpenStreetMap and cannot say which 
if any are correct.

My observations regarding inconsistencies with the coastline and lakes 
are that:
(1) Region and District shapefiles follow the lakeshore for Victoria but 
the lake centreline for Tanganyika and Nyasa.  For statistical mapping 
purposes the boundaries would normally follow the edge of water bodies.
(2) the northern lakeshore for Nyasa follows the coastline but the 
southern boundary follows the centreline.
(3) There is also an error in the most northern section of Lake Nyasa on 
the Malawi side.
(4) I have concerns about the interpretation of the coastline around the 
Rufiji delta, Kilwa and Mafia with regards to the alignment with the 
high/low water mark and tidal areas.
(5) on the Water Body shapefile a number of large and small islands are 
missing in Lake Victoria  e.g. Ukerewe
(6) there inconsistencies in dealing with internal lakes and 
administrative boundaries e.g. Lake Rukwa and Lake Natron, Kagera and 
their delineation.  Some small lakes are included some are not.
(7) there is a strange spike on the coastline south of Mtwara.

I think the NBS and/or Survey & Mapping Division should work together 
and take responsibility for addressing these issues which are major 
problems for GIS users.  If we as users all take it upon ourselves to 
fix these issues independently we will have a real problem resulting in 
many differing datasets circulating around the users of Tanzania GIS data.

It is projected that the Ward and Village boundaries will be released by 
NBS this year, if these issues persist with these datasets then as users 
we will continue to have a real problem.   Do we have any subscribers 
from NBS or SMD that could take forward these data quality issues.

Regards,
Mike

************************************
Mike Shand,
FRSGS; MAppSci; FBCartS,
Honorary Research Fellow
(GIS Cartographer / Consultant)
Geographical & Earth Sciences,
University of Glasgow,
Scotland, U.K.
Tel: +44 (0)141 330 4780
E-mail: Mike.Shand at glasgow.ac.uk <mailto:Mike.Shand at glasgow.ac.uk>
Hon. Secretary:  Society of Cartographers http://www.soc.org.uk/
HOME PAGE & TANZANIA Links: 
http://www.gla.ac.uk/schools/ges/staff/mikeshand/ 
<http://web2.ges.gla.ac.uk/%7Emshand>
************************************

The University of Glasgow, charity number SC004401

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