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.
Map - Malaria Distribution
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. 

Map - Endemic/Epidemic Risk Areas

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.
Map - Duration of Malaria Transmission Season
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.

Map - Start/End of Transmission Season



 

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.

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

Map - Population Distribution



 

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

Map - Administrative Boundaries


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


Back to top

MARA/ARMA home