The gghydro.tar.gz file contains a subset of the Global Hydrographic Data, Release 2.2 (GGHYDRO). The subset is for the LBA-Ecology study area. This README file contains information regarding: 1. Data format 2. Procedure used to create the Amazon subset 3. Legend and data source ------------------------------------------------------------------- DATA FORMAT ------------------------------------------------------------------- The downloadable file, gghydro.tar.gz, is a UNIX compressed tar file. Once the file is untarred there are 19 separate files: 1. gghbas1.dat* --> Major drainage basins, ~30 drainage systems 2. gghbas2.dat* --> Smaller drainage basins, ~150 drainage systems 3. gghcryo.dat* --> Main features of the cryosphere 4. gghdsrf.dat --> Dry surface (% of grid cell) this is equal to the sum of the percentages in gghland.dat, gghswmp.dat, gghdune.dat, and gghsmrs.dat 5. gghdune.dat** --> Sand dunes (% of grid cell) 6. gghflak.dat** --> Perennial freshwater lakes (% of grid cell) 7. gghfriv.dat --> Perennial rivers; stream frequency (counts per grid box) 8. gghglac.dat** --> Glacier ice, including shelf ice excluding pack ice (% of grid cell) 9. gghilak.dat** --> Intermittent water bodies (% of grid cell) 10. gghiriv.dat --> Intermittent rivers; stream frequency (counts per grid box) 11. gghland.dat** --> Exposed land not covered by swamp, intermittent water bodies, glacier ice, sand dunes, saltmarsh or salt flats (% of grid cell) 12. gghms05.dat --> 5 percent land mask; value of 1 is assigned where the sum of gghdsrf.dat, gghglac.dat, gghsflt.dat, and gghilak.dat exceeds 5%, elsewhere value is 0. 13. gghrice.dat --> Annual average of runoff of glacier ice (kg m^-2 yr^-1) for this subset all values are 0 but the file was included for sake of completeness. 14. gghrner.dat --> Estimated root mean square error of gghrnof.dat (%) 15. gghrnof.dat --> Annual average of surface water runoff from land surfaces (kg m^-2 yr^-1) 16. gghsflt.dat** --> Salt flats (% of grid cell) 17. gghsltw.dat** --> Saltwater, whether marine or terrestrial (% of grid cell) 18. gghsmrs.dat** --> Saltmarsh (% of grid cell) 19. gghswmp.dat** --> Swamp, marsh, and other wetlands (% of grid cell) * Categorical data, go to legend section for further information. ** The sum of these nine terrain types (land, flak, swmp, sltw, ilak, glac, dune, smrs, sflt) is 100 for each grid cell. It is highly recommended that you review the original documentation for this data set for more specifics. The original documentation, gghrls22.doc, can be downloaded from the following anonymous ftp site at Trent University: ftp://ftp.trentu.ca/pub/gghydro/ The data files are in ASCII Grid format for ArcInfo. Each file contains a single ASCII array with integer values. Coordinates listed below are in decimal degrees. Rows 35 Columns 55 UpLeftX -85 UpLeftY 10 LoRightX -30 LoRightY -25 cellsize 1 Projection geographic The ASCII file consists of header information containing a set of keywords, followed by cell values in row-major order. The file format is {NODATA_VALUE xxx} row 1 row 2 . . . row n where xxx is a number, and the keyword NODATA_VALUE is optional and defaults to -9999. Row 1 of the data is at the top of the grid, row 2 is just under row 1 and so on. The end of each row of data from the grid is terminated with a carriage return in the file. To import this file into ArcInfo use the following command at an ARC prompt: ASCIIGRID {INT | FLOAT} Arguments - the ASCII file to be converted. - the name of the grid to be created. {INT | FLOAT} - the data type of the output grid. INT - an integer grid will be created. FLOAT - a floating-point grid will be created. ------------------------------------------------------------------- PROCEDURE USED TO CREATE THE AMAZON SUBSET ------------------------------------------------------------------- The original data were obtained and read following the directions in the original documentation. The data were converted to ascii arrays and then imported into ArcInfo using the ASCIIGRID command. Using GRID ( a raster- or cell-based geoprocessing toolbox that is integrated with ArcInfo) the SETWINDOW command was used to define the subarea of interest. This subarea was defined by identifying the bounding coordinates as follows: x_min -85 y_min -25 x_max -30 y_max 10 The "snap_grid" option of the SETWINDOW command was used. This snaps the lower- left corner of the specified window to the lower-left corner of the nearest cell in the snap_grid and snaps the upper-right corner of the specified window to the upper-right corner of the nearest cell in the snap_grid. In this case the snap_grid is the original data grid. The purpose of this is to ensure the proper registration of the newly set analysis window. The command format used is as follows: SETWINDOW x_min y_min x_max y_max original_grid Once the window was set, creating the new grid was simply a matter of setting the new subset grid equal to the original grid. subset_grid = original_grid An ASCII array was created from the new subset grid using the GRID command GRIDASCII. file.dat = GRIDASCII(subset_grid) ------------------------------------------------------------------- LEGEND & ADDITIONAL SOURCES OF INFORMATION ------------------------------------------------------------------- The following legends are used in the original data for the categorical fields: ****bas1.dat**** 32: no land 48: no runoff 49: internal (local/regional) 50: Arctic Ocean 51: Atlantic Ocean 52: Mediterranean Sea 53: Indian Ocean 54: Pacific Ocean 65: Caspian Sea 66: Aral Sea 67: Lake Balkhash 68: Lop Nor 69: Helmand/Seistan 70: Lake Chad 71: Makgadikgadi 72: Lake Eyre 73: Abbe 74: Assale 75: Blanche 76: Bulloo 77: Eyasi 78: Frome 79: Gholkarteniz 80: Issyk Kul 81: Mar Chiquita 82: Nazas 83: Rudolf 84: Rukwa 85: Poopo 86: Tengiz 87: Urmia 88: Van 89: Uvs Nor 90: Hyargas Nor 91: Tsaidam ****bas2.dat**** 32: No land 48: No runoff 49: Internal drainage 50: Arctic Ocean 51: Atlantic Ocean 52: Mediterranean Sea 53: Indian Ocean 54: Pacific Ocean 65: Caspian 66: Aral 67: Balkhash 68: Lop Nor 69: Helmand-Seistan 70: Chad 71: Makgadikgadi 72: Eyre 73: Abbe 74: Assale 75: Blanche 76: Bulloo 77: Eyasi 78: Frome 79: Gholkarteniz 80: Issyk Kul 81: Mar Chiquita 82: Nazas 83: Rudolf 84: Rukwa 85: Poopo 86: Tengiz 87: Urmia 88: Van 89: Uvs Nor 90: Hyargas Nor 91: Tsaidam 97: Anabar 98: Back 99: Churchill (Manitoba) 100: Colville 101: Hayes 102: Indigirka 103: Kazan 104: Khatanga 105: Kolyma 106: Lena 107: Mackenzie 108: Nelson 109: Ob 110: Olenek 111: Onega 112: Pechora 113: Pyasina 114: Severnaya Dvina 115: Albany 116: Taymyr 117: Thelon 118: Yana 119: Yenisei 120: Pur-Taz 121: Parana 122: Moose 123: Alabama 125: Brazos 128: Amazon 129: Chubut 130: Churchill (Nfld) 131: Cuanza 132: Cunene 133: Douro 134: Ebro 135: Elbe 136: Essequibo 137: Gambia 138: Garonne 139: Jequitinhonha 140: Koksoak 141: Loire 142: Magdalena 143: Mississippi 144: Neva 145: Niger 146: Oder 147: Ogoue 148: Orange 149: Orinoco 150: Parnaiba 151: Rhine 152: Rio Grande 153: Saguenay 154: Sanaga 155: Sao Francisco 156: Senegal 157: St Lawrence 158: Tocantins 159: Uruguay 160: Vistula 161: Volta 162: Zaire 163: Zapadnaya Dvina 164: Danube 165: Dnepr 166: Dnestr 167: Don 168: Nile 169: Rhone 170: Brahmaputra 171: Euphrates 172: Ganges 173: Godavari 174: Indus 175: Irrawaddy 176: Juba 177: Krishna 178: Limpopo 179: Mahanadi 180: Murray-Darling 181: Rufiji 182: Salween 183: Tigris 184: Zambezi 185: Amur 186: Anadyr 187: Chao Phraya 188: Colorado 189: Columbia 190: Fraser 191: Hwai 192: Hwang Ho 193: Kuskokwim 194: Liao 195: Mekong 196: Pearl 197: Red 198: Rio Grande de Santiago 199: Yangtze 200: Yukon 201: Kura 202: Ural 203: Volga 204: Amu Darya 205: Syr Darya 206: Cooper 207: Warburton 208: Bandama 209: Save 210: Ruvuma 220: Baltic 221: Black Sea 222: Red Sea 223: Persian Gulf 224: Hudson Bay-Foxe Basin 225: Gulf of Mexico 226: San Francisco Bay ****gghcryo.dat**** 32: water without ice cover 48: permafrost absent or extremely restricted 49: permafrost restricted 50: permafrost common 51: permafrost ubiquitos 53: permanent sea or lake ice 54: seasonal sea or lake ice 55: ice shelf 57: ice sheet Although not all of these categories may be represented in the subset of the data, the original legend has been retained. The original data and documentation may be downloaded from the anonymous ftp site at Trent University: ftp://ftp.trentu.ca/pub/gghydro/ ------------------------------------------------------------------- ORIGINAL DATA SET CITATION ------------------------------------------------------------------- Cogley, J.G., 1998, GGHYDRO -- Global Hydrographic Data, Release 2.2. Trent Climate Note 98-1, Department of Geography, Trent University, Peterborough, Ontario, Canada. Data available on-line at ftp://ftp.trentu.ca/pub/gghydro/ ------------------------------------------------------------------- SUBSET DATA SET CITATION ------------------------------------------------------------------- LBA study area subset of, Cogley, J.G., 1998, GGHYDRO -- Global Hydrographic Data, Release 2.2. Trent Climate Note 98-1, Department of Geography, Trent University, Peterborough, Ontario, Canada. Available on-line at ftp://www-eosdis.ornl.gov/data/lba_regional/gghydro/