Fig. 2
Projection bias assessment. Graphical representation of the difference in terrain slope calculation due to the effect of using the World Geodetic System 1984 (WGS84) (raster panels right-hand side) compared to the Equi7 projection (raster panels left-hand side). A study area located in the subtropical zone (image centre: longitude −83.26, latitudes 9.05) was used to subset the MERIT-DEM for an area of 500 × 500 grid cells (g). This area has been transposed to a subarctic zone (image centre: longitude −38.19, latitudes 72.80) under the Equi7 projection (a). After having been reprojected to WGS84 (b,h), the variable slope was calculated in the four conditions (c–f), and then reprojected back to Equi7 for comparisons (see blue line-arrows). The scatter plots on the right-hand side shows the WGS84-MERIT slope (d,f) vs. the MERIT slope under the Equi7 projection (c,e), respectively for the subarctic zone (i) and for the subtropical zone (j). The red lines represent the 1:1 relationship and black lines represent a linear model between the two axes. The slope calculated under WGS84 in the subarctic zone is clearly underestimated compared to the one calculated under the Equi7 projection.
