[Proj] Re: Mapping Africa in an equal area projection

[Corrado Topi]

Thanks Daan!

What ellipsoid / datum, would you choose? WGS84, ETRS89, or waht else?

Regards


strebe at aol.com wrote:

> 
>  Corrado:
> 
> 
> 
>  Of the candidates you list, I would call Mollweide inappropriate because
>  it stretches Africa north-south to in order to reduce distortion
>  elsewhere. It really is best left for world maps, where that compromise
>  results in some benefit. Any of the others you list could be reasonable,
>  depending on how they are constructed.
> 
> Because Africa spans roughly
> the same latitudinal range north as south, an equatorial Lambert
> azimuthal equal-area is a fine choice, and will give you the lowest
> distortion of the group. Nor are there any better projections to recommend
> without going exotic. Sinusoidal is not a common modern choice, and I do
> not recommend it in this case because you will end up with higher
> distortion around the periphery than the other projections, and with no
> compensation.
> 
> Unless your application would benefit from straight parallels and
> meridians, or unless your two standard parallels happen to be exactly
> latitudes of opposite sign, then Albers will always perform better than
> cylindric equal-area. But the advantages of Albers are largely lost on
> Africa unless you were willing to do something exotic like a heavily
> oblique aspect. Left with its standard parallels set to the graticule
> parallels, it would end up very similar to the cylindric equal-area
> (because the two standard parallels would be nearly latitudes of opposite
> sign), and in that case it cannot approach Lambert for low distortion
> across your region of interest.
> 
> Regards,
> — daan Strebe


-- 
Corrado Topi

Global Climate Change & Biodiversity Indicators
Department of Biology, University of York, UK