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ArcGIS has both Densify and Geodetic Densify tools. The help pages do not describe the tools well enough to determine when and where each is the most appropriate choice.

When and where should we use Geodetic Densify over Densify and vice versa?

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Densify - 2D Cartesian based on the data's coordinate system. It had better be projected, unless the data has a small extent (and possibly not at mid- to high-latitudes). It's fine for densifying lines or polygons for a city, county, or small state when the data is in a reasonable projected coordinate reference system. Never use it if the data is in a geographic coordinate reference system.

Use Densify when you want to maintain the "straightness" of the lines--like streets or parcel boundaries, things like that. It could include cases where you have lat/lon, but you want to densify along the latitude line--think the US-Canadian border in the west

Geodetic Densify - Densifies on the ellipsoid surface using any of four options, so more accurate for larger extents or at mid- to high-latitudes. The calculations are performed on the ellipsoid associated with the input data's coordinate system.

Before and after Densify are the same rendered in pseudo-Plate Carree projection. The picture looks the same--straight line segments because the world is treated as if it's flat:

straight line segments

After Geodetic Densify the lines are curved when displayed in pseudo-Plate Carree:

after geodetic densify

(pictures cropped from Esri help topic)

  • Thank you. To clarify re: pictures: in the GD help page, the first picture shows the original shape. A Densify operation on that would increase the number of vertex points but the shape would remain unchanged when shown in pseudo-Plate Caree. Whereas Geodetic Densify would increase the number of points AND change the shape when drawn in pseudo Plate Caree, as shown in 2nd picture? – matt wilkie Jun 5 '17 at 21:11
  • The Silverlight API has a really good explanation of Geodesic Densify, much better then the other help topics (mentions what ellipsoid is used for example). Do you know if this method is identical to the geoprocessing GD tool? (note t vs s) – matt wilkie Jun 5 '17 at 21:17
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    Under the geodetic_type parameter: "Geodetic calculations are performed on the ellipsoid associated with the input data's coordinate system." They're likely both calling Esri projection engine in the end, but I'd have to run numbers because Silverlight is using "great circle" rather than "geodesic". Great circle means on a sphere, not an ellipsoid. – mkennedy Jun 5 '17 at 23:13
  • re: your first comment on the pictures. After Densify, the first picture would still look the same--straight line segments because the world is treated as if it's flat. – mkennedy Jun 5 '17 at 23:14
  • Thank you for the clarifications. I see much more clearly now. Another way of asking the question: since Geodetic is so much smarter, shouldn't we just use it all the time? Are there situations where Densify is the better choice? – matt wilkie Jun 5 '17 at 23:24

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