R Script To Download Hydrosheds Dem
This section provides only a brief overview regarding data availability, layers, and formats of the HydroSHEDS database.
For more information please refer to the Technical Documentation.
Data availability
The HydroSHEDS database provides a suite of raster and vector datasets, covering many of the common derivative products used in hydrological analyses. The HydroSHEDS data layers are being developed for all landmasses of the globe from 56° South to 84° North (i.e. excluding Antarctica). The data is prepared in seamless mode (no edge effects) and is provided as global or regional maps, or in 5-degree by 5-degree tile coverage.
HydroSHEDS is produced on a continental basis. The drainage direction maps—which represent the primary data layer from which all other products are derived—have been completed or are scheduled for release as follows:
| Original regions (56°S to 60°N) | |
| South America | Completed (May 2006) |
| Central America (Mexico and Caribbean) | Completed (March 2007) |
| Asia | Completed (March 2007) |
| Africa | Completed (October 2007) |
| Australasia | Completed (March 2008) |
| Europe and Middle East | Completed (October 2008) |
| North America (USA and Canada) | Completed (January 2009) |
| Appended regions (north of 60°N) | |
| Arctic (northern Canada) | Scheduled for December 2015 |
| Scandinavia and Iceland | Scheduled for December 2015 |
| Siberia | Scheduled for December 2015 |
| Greenland | Scheduled for December 2015 |
Data layers
At this time, HydroSHEDS provides several core data layers at 3 arc-second, 15 arc-second, and 30 arc-second resolutions, including elevation surfaces, drainage directions, river networks, and watershed boundaries. Additional data layers are under construction, and future data developments are planned. Currently, the following data layers and resolutions are available:
| Index | HydroSHEDS data layer | Format | Resolution(s) |
|---|---|---|---|
| DEM | Void-filled elevation | Raster | 3 sec, 15 sec, 30 sec |
| CON | Hydrologically conditioned elevation | Raster | 3 sec |
| DIR | Drainage directions | Raster | 3 sec, 15 sec, 30 sec |
| ACC | Flow accumulation (number of cells) | Raster | 15 sec, 30 sec |
| RIV | River network (lines) | Vector | 15 sec, 30 sec |
| BAS | Drainage basins (polygons) | Vector | 15 sec, 30 sec |
As the primary data layer, the drainage direction maps define the direction of flow from each cell in the conditioned DEM to its steepest down-slope neighbor. Values of flow direction vary from 1 to 128. All final outlet cells to the ocean are flagged with a value of 0. All cells that mark the lowest point of an endorheic basin (inland sink) are flagged with a value of -1. The flow direction values follow the convention adopted by ESRI's flow direction implementation.
Data formats and distribution
File name syntax
HydroSHEDS provides data in various regional extents, types, and resolutions. Information about the content is provided in the file names which follow the naming convention <Region_DataType_Resolution>.
Extent
File names of layers with continental extent are defined by a two-digit identifier:
| Identifier | Region |
|---|---|
| Af | Africa |
| As | Asia |
| Au | Australasia |
| Ca | Central America (Mexico and Caribbean) |
| Eu | Europe and Middle East |
| Na | North America (USA and Canada) |
| Sa | South America |
To facilitate electronic distribution, all raster data at 3 arc-second resolution have been divided into 5-degree by 5-degree tiles. For example, the area of South America is covered by 103 individual tiles. The tile names are defined by a 7-digit identifier which refers to the latitude and longitude of the lower-left (southwest) corner of the tile. For example, the coordinates of the lower-left corner of tile s15w065 are 15 degrees south latitude and 65 degrees west longitude.
Data type
| Identifier | Type of data |
|---|---|
| DEM | Digital Elevation Model (void-filled) |
| CON | Hydrologically conditioned elevation |
| DIR | Drainage directions |
| ACC | Flow accumulation (number of cells) |
| RIV | River network (stream lines) |
| BAS | Drainage basins (watershed boundaries) |
Resolution
| Identifier | in sec/min | in degree | in meters/km |
|---|---|---|---|
| 3s | 3 arc-second | 0.000833333333333 | approx. 90 m at the equator |
| 15s | 15 arc-second | 0.004166666666667 | approx. 500 m at the equator |
| 30s | 30 arc-second | 0.008333333333333 | approx. 1 km at the equator |
| 5m | 5 minute | 0.083333333333333 | approx. 10 km at the equator |
Note that all data provided in 5-degree by 5-degree tiles is in 3 arc-second resolution. However, the extension <3s> is omitted in order to shorten the file names.
File formats
The vector data sets distributed with HydroSHEDS are being made available in ESRI Shapefile format. A HydroSHEDS shapefile typically consists of five main files (.dbf, .sbn, .sbx, .shp, .shx). The raster data layers distributed with HydroSHEDS are being made available in two different formats: (a) in ESRI GRID format, and (b) as binary raster image in ESRI Band Interleaved by Line (BIL) format. The ESRI GRID format is supported within ESRI's ArcGIS software environment, but it can also be imported into various independent GIS packages. The simple BIL format should allow for easy ingest into most popular image processing and geographic information systems packages. More details about the file formats are provided in the Technical Documentation.
HydroSHEDS data is distributed in compressed zip file format. To use the data files, the zip files must first be decompressed. Each zip file includes a copy of the HydroSHEDS Technical Documentation (but note that some files include the outdated version 1.0 of the Technical Documentation). Multiple zip files that contain data in ESRI Shapefile or BIL format can be decompressed into one folder. Multiple zip files that contain data in ESRI Grid format are by default decompressed into separate subfolders. To store multiple grids in one root folder, the grids have to be copied or moved from within an ESRI compatible software application.
Source: https://www.hydrosheds.org/page/availability
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