Information on Maps
MALARIA
Distribution
Model
Seasonality
Model
Prevalence
Models
OTHER
Population Distribution
Administrative Boundaries
Topographical Features
Distribution
Model
Background
This map is a theoretical model based on available long-term
climate data. It has a resolution of about 5x5 km. Although it is reasonably
accurate, it is not based on actual malaria data and may
not reflect the real malaria status.
It shows the theoretical
suitability of local climatic, and therefore the potential distribution
of stable malaria transmission in the average year.
Please note that climatic
conditions, and therefore malaria transmission, vary substantially from one year
to the next. Malaria control activities can also dramatically alter the malaria
transmission situation. |
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Meaning
Where climate is “suitable” (red = 1), malaria is likely endemic
(hypo-, meso-, hyper- or holoendemic).
“Suitable” areas may have little or no malaria because of malaria control.
Where climate is “unsuitable”
(white = 0), malaria is likely epidemic or absent.
Some “unsuitable” areas may actually have endemic malaria because of
the presence of surface water in an area where there is little or no rain.
In the marginally suitable
areas (0.1 - 0.9) transmission may occur at steady but low levels (eg eastern
Africa), or in strongly seasonal cycles with great inter-annual variation
(eg western & southern Africa).
More information
For more detailed information please see the relevant section in the
MARA/ARMA technical report (Click
here).
Endemic / Epidemic Risk Areas
Background
The malaria distribution model has been
re-classified into endemic and epidemic areas. These risk areas have then
been used to calculate the number of people living in endemic and epidemic
conditions.
In Southern Africa
(Namibia, Botswana, Zimbabwe and South Africa) "endemic" encompasses regions
where the climate is 50-100% suitable, whereas in the rest of Africa "endemic"
refers to regions where climate is 20-100% suitable. Different cut-offs
were used, because in southern Africa malaria is at the limit of its distribution
and has been largely reduced through malaria control.
Otherwise, all comments
on the malaria distribution model apply to this map also.
Meaning
Endemic areas are defined as "areas with significant annual transmission,
be it seasonal or perennial". Epidemic areas are defined as "areas prone
to distinct inter-annual variation, in some years with no transmission
taking place at all".
Since this is a theoretical model, areas
defined as "endemic" may be "epidemic" in reality, or v.v. |
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More information
See Snow et al. 1999. Bull. WHO 77: 624-640.
Duration of Malaria Transmission Season
Background
These maps are also theoretical models based on available
long-term climate data. They have a resolution of about 5x5 km. Although
they are reasonably accurate, they are not based on actual malaria
data and may not reflect the real malaria status.
They are based on the theoretical
suitability of local climatic, and therefore the potential duration, onset
and end of the malaria transmission season, in the average year.
Please note that climatic
conditions, and therefore malaria transmission, vary substantially from
one year to the next. Malaria control activities can also dramatically
alter the malaria transmission situation. More work is ongoing to refine
these models. |
 |
Meaning
In the Months of Risk model, malaria transmission is strongly
seasonal to epidemic (yellow = 1-3 months), seasonal and
endemic (light green = 4-6 months) or perennial and endemic
(dark green = 7-12 months). Some areas shown as "No transmission" (white)
may actually have endemic malaria because of the presence of surface water
in an area where there is little or no rain.
More information
For more detailed information please see the relevant
section in the MARA/ARMA technical report (Click
here).
Start / End of Transmission Season
Background
Based on the seasonality model, these maps
simply reflect the first and last month of the average transmission season.
All comments on the seasonality model apply to these maps too.
Meaning
The colours indicate the month in which the transmission season starts
and ends, in the average year. In a few areas there are two transmission
season, so that there are two start and two end of season maps.
Malaria
Prevalence Models
Background
These are statistical / spatial models based on empirical malaria
prevalence data. These models are the results of data analyses
carried out on the MARA/ARMA data, by different groups and people at different
times, and even using different methods.
These models analyse
the malaria data against some environmental determining factors (such as
climate, altitude, vegetation cover, agro-ecological zones, etc.). The
level of prevalence is then predicted for the entire country or region,
based on the established relationships between malaria prevalence and environmental
data. |
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Meaning
Where prevalence is >75% malaria is holo-endemic; where
prevalence is between 51 and 75% malaria is hyper-endemic,
where prevalence is between 11 and 50% malaria is meso-endemic,
and where prevalence is < 10% malaria is hypo-endemic.
These categories, proposed by
Metselaar and Van Theil (1959, Tropical and Geographical Malaria
11:157-161)
are artificial and some models use different categories.
The development of such
empirical models is still ongoing, and some models already available as
maps, are still likely to change as more data comes in.
More information
For more detailed information about the transmission
intensity models, please see the relevant section in the MARA/ARMA technical
report (Click here), or the
report on the West African modelling workshop (Click
here).
Population Distribution
Background
This map is a population model, produced by Uwe Deichmann, and is based
on the best census data that were available from each country. The accuracy
of the data vary from good census data to unconfirmed estimates.
In the model the population in
each administrative region has been re-distributed, so that predicted population
density is concentrated around towns and along the transportation network.
Thereby the the resolution of population data is improved.
More information
For more information see
http://grid2.cr.usgs.gov/globalpop/africa/Africa_index.html |
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Administrative Boundaries
Background
National and sub-national boundaries were originally obtained from
the African Data Sampler, a CD-ROM published by the World Resources Institute
(WRI), 1995, 1709 New York Ave., NW, Washington, DC 20006, USA.
These boundaries are then updated
when and where more recent maps were available (eg updated national
boundaries in Tanzania, Malawi, Kenya; updated sub-national boundaries
in South Africa and Tanzania). More information
For the African Data Sampler, see the WRI homepage:
http://www.wristore.com/afdatsamgeor.html |
 |
Topographical data
Background
All topographical data is taken from the African Data Sampler, a CD-ROM
published by the World Resources Institute (WRI), 1995, 1709 New York Ave.,
NW, Washington, DC 20006, USA.
Topographical data available
in the African Data Sampler includes populated places and settlements, roads,
rivers and streams, lakes, elevation contours and many more.
More information
For the African Data Sampler, see the WRI homepage:
http://www.wristore.com/afdatsamgeor.html
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