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Section 2.2, NHD Availability, describes how NHD databases are distributed by HUC basins. For CDSS, <br />it is necessary to merge the NHD data files to create statewide (or at a minimum, division) databases. To <br />navigate streams, the data sets must contain full basins that do not end at the state border. Currently NHD <br />does not include trans-basin features. <br />The USGS is planning to distribute the NHD by state on DVD; however, statewide databases are not <br />currently available and therefore merging databases for use in CDSS is necessary. The general procedure <br />for merging NHD databases is as follows: <br />Download the personal geodatabase (.mdb) for the regions of interest. Download medium- <br />resolution data (100k) where high-resolution data (24k) are not available. The NHD data are <br />distributed by sub-basin (HUC 8 digits) or sub-region (HUC first 4 digits). Full coverage of the <br />state with minimum number of separate geodatabases can be achieved by downloading by <br />subregion. Figure 3.1 is a screen image of the NHD viewer showing the 17 sub-regions <br />covering the state of Colorado labeled with the 4-digit HUC. <br />Start ~ -~~~ ~C~~jtemp~... NHD Geo... "NHD Tec... ~MicrosoFt... ®~nhd.doc ~~. ®~log.doc untitled -... ~~pisplay... <br />Figure 3.1. NHD Viewer Screen Image. Pre-staged personal geodatabases by sub-region at medium resolution <br />are available for download on the NHD ftp site. Error! Reference source not found lists the 100K database files <br />for the Colorado subregions. It is estimated that 24K resolution data have file sizes several times larger than the <br />100K resolution files. <br />2. Select a geodatabase to serve as the starting point. <br />Page 8 of 17 ~IZlverslde Technnlo~yv Inc. <br />4s':rkv Resuurce.s Ergrnee: mg end ~C9 nsuNrng <br />