I have a Aster DEM, and from that i get the drainage network, and now i need to calculate the drainage area, but i don't know if the drainage area is equal to the basin area.

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    That is not a GIS question, but a geomorphology or Hydrology related. It shows no research about the subject in question. A simple google search gives a perfect explaination that clarifies this issue: greenfacts.org/glossary/def/drainage-area.htm – dof1985 Jan 16 '15 at 17:38
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    I disagree, this most certainly is a GIS question. GIS is by far the most common environment in which drainage areas, or basins, are mapped these days. There are plenty of questions on the GIS.SE related to upstream drainage area. – WhiteboxDev Jan 16 '15 at 18:11
  • @WhiteboxDev, I agree with you mostly. Yet that is a fundamental question that asks for a definition, not even a GIS technical one. It shows no research at all, and should be voted down - for the sake of GIS.SE users and quality of this forum. It took me 1 minute to find an answer for this question including reading it. – dof1985 Jan 16 '15 at 18:41
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    @dof1985 the OP has clearly stated that they have a DEM and are performing automated stream mapping with the data. This is very clearly within the realm of the field of GIS, in fact I would say it is geomorphometry or digital terrain analysis. It may fall outside of your usual application area within GIS, but it is a very wide field. – WhiteboxDev Jan 16 '15 at 18:51
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    @dof1985 Also, I'm not disagreeing with you that the question could have demonstrated more research but I am stating that it falls well within topic of the forum. The process of DEM based stream mapping involves creating a drainage area (flow accumulation) raster. It would be quite easy for someone, given the number of variations on what this raster is called, to be confused over its exact definition. So I think the question is perfectly valid. It's best not to discourage new members from asking questions here. – WhiteboxDev Jan 16 '15 at 18:56

If I've interpreted your question correctly, it sounds to me like you are interested in deriving a network of stream lines (drainage network) from a DEM. If this is the case, then the drainage area that you are referring to is actually a raster of upslope contributing area (also known as the specific catchment area or flow accumulation). The flow accumulation grid is essentially a raster that shows for each pixel the number of pixels (or area) that lie upslope of the pixel and that are connected to it through a flow path. The value of flow accumulation is a monotonic step function increasing downslope such that river valley bottoms tend to have considerably higher values than their adjacent hillslopes. This is the reason these rasters are used for automated DEM based stream mapping. A drainage basin, or in some places what is more commonly known as a watershed, is the area that drains to a single point, usually an outlet point along a stream network. They are related concepts and easy to confuse, particularly given how many regional synonyms each term has.

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Don't worry about the downvotes. Sometimes people forget that GIS is applied to the study of biophysical phenomena just as often as it is applied to social phenomena. It's a very diverse field!

  • You're right that GIS software can be applied to many different studies. I personally see GIS software as a spatial-analysis program first (before considering its geographic capabilities), this post contains a few examples for using GIS software in completely different fields of study. – Joseph Jan 19 '15 at 16:34

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