6

In hydrologic terrain analysis is there a difference between "pits" and "depressions"?

For instance, Planchon and Darboux (2002) state

The usual numerical methods for removing the depressions of a Digital Elevation Model (DEM) gradually fill the depressions and merge the embedded ones.

While Grimadli et al (2007) states

Spurious pits in digital elevation models (DEMs) are traditionally removed by filling depressions, often creating flat regions that lead to inaccurate estimation of landscape flow directions. In this study, a physical approach based on a simple landscape evolution model is proposed for DEM pit removal.

  • This is my opinion but I think this is just semantics, from a processing perspective (getting the job done) they are the same thing, a cell where the surrounding cells are higher. There are different ways to fill that pit which I guess is what the papers you are referencing are referring to? – Hornbydd May 2 '16 at 19:23
  • Another word for them is "sinks". – Dan C May 2 '16 at 19:32
  • @Hornbydd: from a processing perspective there may be a great deal of difference between single- and multi-cell features in terms of the appropriate algorithms and speed of processing. – Richard May 2 '16 at 19:37
11

There is a difference, and I recommend the typology presented by Lindsay (2015) be used.

Lindsay (2015) presents a typology which defines a pit as a single cell in a DEM whose elevation is below that of the surrounding cells and a depression as a region of cells which drain inwards to a pit. This is consistent with the definitions used by O'Callaghan and Mark (1984) in one of the earliest papers applying algorithmic approaches to digital elevation models: "a pit is defined as a point none of whose neighbors have lower elevations" and "the 'overflow' point was defined as the point which was on the boundary of the basin and which had the minimum elevation difference to the pit."

Lindsay (2015) Depression, Sink, Pit, Flat Typography

To establish the relative frequency of terms, I performed a quick literature search.

The term "depression" is used in the above sense by Jenson and Domingue (1988), Martz and Garbrecht (1999), Planchon and Darboux (2001), Jones (2002), Otto and Thurnherr (2007), Yong-He et al. (2009).

The words "pit" and "depression" appear to be used interchangeably by Jenson and Trautwein (1987), Ehlschlaeger (1989), and Grimaldi (2007).

The word "minima" has also been used to mean both depressions and pits by Vincent and Soille (1991) and Soille and Gratin (1994). The word ``sinks" has been used to mean both depressions and pits by Olivera et al (2000) as well as the ESRI corporation in various ArcGIS guides.

A minority of authors used only the word pit: Tarboton et al (1991) and Soille (2004).

  • 3
    I really like this answer ;-) Couldn't have said it better myself! Oh, and for a preprint of the Lindsay paper, for those who can't get access from behind the paywall, you can go to: uoguelph.ca/~hydrogeo/publications.html – WhiteboxDev May 2 '16 at 19:52
  • Thanks, @WhiteboxDev: I really appreciated that diagram. I'm hoping it has a clarifying effect. – Richard May 2 '16 at 19:54
  • 3
    Me too. After years of working in the field, I was a little tired of the confusion of terms. Now if only we could come to a consensus on the usage of the terms DEM, DSM, DTM. – WhiteboxDev May 2 '16 at 19:56

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