Elevation-Derived Hydrography READ Rules: Additional Elevation-Derived Hydrography Treatments and Elevation Specific Features
The following describes treatments and additional features that shall be applied during the acquisition of Sea/ocean, and other waterbody features and shall be taken into consideration as treatments for the depiction of waterbodies. The treatments and additional features can also be used to convey additional information about the level of confidence for elevation data in certain acquisition areas.
Island
A permanent island is an area of exposed land, surrounded by water (Figure 75). Islands need to be erased from Lake/pond, Stream/river, and Sea/ocean features.
Delineation
Lake/pond
The minimum size for islands within Lake/pond is 0.12 acres (500 square meters).
Sea/ocean
The minimum size for islands within Sea/ocean is 1 acre (4,000 square meters).
Stream/river
The minimum size for islands within Stream/river polygon is 0.12 acres (500 square meters) with the following exceptions:
• The island is present in the hydroflattening breaklines, in which case it may be included.
• There is a group of islands under the minimum size that are grouped close together. They may be added as one island.
See Artificial Path Representation Rules for information about adding Artificial path features in areas with islands.
Island/Sandbar
Intermittently/partially submerged islands or parts of islands are submerged at the time of collection (Figure 76) are most often found in coastal areas because of tidal variations during the collection, or in rivers collected while at a high flow. If island/sandbar is disconnected from the shore or is visible at the time of collection, then treat as an island (remove from Lake/pond or Sea/ocean feature). Otherwise, treat as shoreline.
