The data produced by GIRAS was originally collected at a scale of 1:250K. Some areas, notably major cities in the west, were recompiled at a scale of 1:100K. In order to join the data together and use the data in a geographic information system (GIS) the data were processed in the ARC/INFO GUS software package. Within the GIS, the data were edgematched and the neatline boundaries between maps were removed to create a single data set for the conterminous United States.
HUC, GIRAS, Hydrologic Units, 1:250
Original Huc Data was clipped to CO Water Division 1.
After the files for a given section were all converted into ARC/INFO format, a loop aml was run which copied a coverage and its neatline cover into temporary storage (there was not enough room in info to deal with a large number of files in one directory), attached to that directory, built line topology, and went into the editor, ARCEDIT. In ARCEDIT, the outer edge (original neatline) was selected and deleted an the mathematically-calculated neatline coverage from the GIRASNEAT AML program was copied in using the ARCEDIT GET command. The original neatline was replaced with a calculated neatline because in all cases, the outline of the coverage quad never quite conformed to a "true" neatline causing overlaps and gapes between adjacent maps. The new neatline was connected to the internal arcs where they intersected. Lines which did not quite join the new neatline were extended to the edge with a maximum tolerance of 500 meters. All extensions were made within this tolerance. All arcs which extended beyond the new neatline were clipped off within a 500 meter tolerance as arguments to the CLEAN command into a separate directory. Both the neatline and huc coverages were deleted from the temporary space, and the program looped to the next coverage.
Another program was then run which added an item to the .aat called OUTER, went into INFO, and populated the attribute for all arcs composing the new neatline. This was done by reselecting for the identity of the polygon to the left or right of each arc whose value was "1", the identity of the outer "universe" polygon (reselect lpoly# = 1 or rpoly# = 1 in the .aat and calculated outer to = 1). All coverages were checked for additional dangles and then a MAPJOIN was run using NET as the feature option. Finally, most map edge lines were removed from the MAPJOINed coverage using the DISSOLVE to create a seamless basin coverage with polygons (basins) and arcs (boundaries) with attributes.
Quality control methods were applied to the resulting coverage by detecting and fixing node and label errors and remaining neat line arc problems (i.e. long neat lines still in the coverage). Many more problems arose in the western part of the country than in the east. Bordering HUC code disagreements between quads caused a number of cases in which neatlines did not dissolve. These were provisionally corrected for the most part, however there were several cases that required external review and editing to fix, and are now incorporated in the final data set. After all 1:250K sections were completed, the same procedure was run for the handful of 1:100k quads. These were mapjoined with the 1:250k quads to provide more detailed coverage where it was available.
Revisions: Revision #1. See above for all the details Process_Date 10/92 Revision #2. Seattle and Bakersfield quadrangles were missing from the composite supplied by Pete Steeves. These were manually pasted in using Arcedit with small tolerances. Labelerrors were remedied and most dangles were removed using the Eliminate command. Process_Date 1/93 Revision #3. The following changes were made to a 1:250,000-scale version derived from National Mapping Divisions Geographic Information Retrieval and Analysis System (GIRAS) data. The discrepancies in the hydrologic unit codes (HUCs) in California were changed because the California State Hydrologic Unit Map (HUM) was revised in 1978 but the 1:250,000-scale digital dataset was not. This has been reviewed by Bill Battaglin, Doug Nebert, and Paul Kapinos and is noted under Reviews (#6 below).
The areas in which the HUC labels were incorrect in California were 180701, 180702, 180703, 180600, 180300, and 180400. Boundaries were added in 180702 and 180600 from the 1:2 million source. Along the Oregon/California border, a boundary was added in 180102. In Wyoming, a boundary was added in 100902 from the 1:2 million source. Labels were corrected in these HUCs to reflect state updates, and where necessary, to add new labels to the newly-drawn boundaries. Map edges were manually removed in Arkansas, California, and along the Oregon/California border.
After the changes were made and saved in Arcedit, the build and clean commands were executed, followed by labelerrors. Three polygons had duplicate labels and were corrected. The labels were centered in the polygons by the centroidlabels command. Verification of the coverage was done by the describe command. Process_Date 12/93. Revision #4. The NAMES file was added to the data set and its attributes were defined in the ATT file of the documentation. This table is a lookup table to correlate the 8-digit numbers with verbose names officially assigned to the basins. Process_Date 3/94. Revision #5. The following corrections were made to the 1:250,000-scale coverage of Hydrologic Unit Codes (HUC250):
Valid HUC code, 7140103, added to HUC250.NAM. Bourbeuse, Missouri. HUC250.NAM was sorted on HUC.
HUC frequency >1, tiny polygons were deleted that were erroneous:
17010212 deleted small poly to NW of main poly 10130305 deleted small poly to S of main poly 10230005 deleted small poly to S of main poly 14020001 deleted small poly to N of main poly 15050201 deleted small poly to W of main poly 04080203 deleted small poly to N of main poly 03120001 deleted small poly to S of main poly
Invalid HUC codes, not in names file, were corrected:
18020023 HUC should be 18020111 (in N-central California) 18070010 HUC should be 18070303 (in so. California) 15010017 HUC should be 15010007, delete arc separating it (in nw Arizona) 1870201 HUC should be 18070201 (in so. California, missing an 0) 1870204 HUC should be 18070204 (in so. California, missing an 0) 18060012 HUC should be 18060011 (in so. California, improper polygon closure)
18060011 HUC label added after polygon closure of 18060011
HUC frequency >1, larger polys were checked and corrected:
18020126 western poly is 18020108 in HUC2M (CA) 18050005 southern poly is 18050006 in HUC2M (CA) 18060006 split into 2 polys, no apparent reason, delete arc splitting polys (CA) 04110001 and 04100001 together are 04100001 in HUC2M (MI) (MAPEDGE was deleted) 02080108 northwestern poly is 02080208 in HUC2M (VA)
The invalid HUC codes, and 7140103 were found by relating to the HUC250.NAM file, and identifying polygons with no match in the names file. The rest were found by looking at the 96 polygons which had HUC codes with frequencies >1 in the PAT. Most of these seemed to be correct, and were along the US-Canada boundary, or were islands along the coasts.
These errors were found in the HUC250 coverage published as OFR 94-0326. Process_Date 12/94 & 1/95 Reviews_Applied_to_Data: Peer review, 10/18/93, Bill Battaglin, USGS-WRD, Lakewood, Co, memo to Doug Nebert: ---------------------------------------------------------------------- "I have completed a review of the 1:250,000 scale hydrologic units coverage (HUC) and found the digital data and metadata to be of high quality. I have a few suggested improvements to the digital data and to the documentation. Below is a summary of the methods I used to check feature accuracy in the digital data base and the problems I found.
Digital Features:
The line work for the HUC coverage was checked against the line work from:
(1) the 1:2,000,000 HUC coverage by plotting both data sets out on one large graphic (about 1:3,000,000). No major discrepancies were found except in coastal areas where the 1:2,000,000 scale coverage had more detail than the 1:250,000 scale coverage.
(2) line work from 1:24,000 scale digitized drainage basins in Colorado, Illinois, and New Jersey. The match was generally good with departures generally less than 2500 meters. The biggest departures were in Colorado and were as large as 4000 meters.
(3) line work from the 1:2,000,000 scale rivers coverage for the USA by plotting both data sets out on one large graphic (about 1:3,000,000). In general the nesting of streams in HUCs was good and HUC boundaries inter- sected streams at stream intersections. In some places (SE New Mexico, SE California and NW Utah), the streams coverage does not match the HUC coverage that well, but this could easily be because of the unusual nature of streams in these areas or because of inaccuracies in the streams coverage.
(4) line work from 1:100,000 scale streams from Colorado, Illinois, and Kansas. The nesting of streams in HUCs was very good. Stream arcs for the most part did not cross HUC arcs except at stream intersections. The error (distance from intersection to HUC line) between HUC lines and stream intersection was less than 500 meters at all intersections checked (about 25).
Problems with Line work:
(1) There was a very large number of very short arcs in the coverage (3211 Lt 1000 meters long and 1729 Lt. 100 meters long). Most of these arcs were internal (did not border on outside polygon) and coded as 250k edges(3) (almost 3000) but some were 250k (2) lines and one was a 2m dlg (4). Arcs with lengths of less than 100 meters (maybe even less than 1000 meters) are difficult to deal with when editing subsets of the coverage, and they also add to the overall size of the database. I know many of these lines were created in the process of edgematching the quads, but I think the informa- tion content of these very short arcs is less valuable than the hassle and overhead involved in keeping them in the coverage.
(2) The edit distance for the coverage was set to a very small value. This may have been required for earlier processing, however, it makes the finished coverage difficult to work with. I had to reset the edit distance to a larger value when I wanted to select arcs in ARCEDIT interactively. This, of course, will be one of the things users will want to do with the new HUC coverage.
Polygon labels/attributes:
(1) Label point accuracy was checked by making a point cover of polygon labels from the 1:2,000,000 HUC coverage and then doing an identify of those points in the 1:250,000 scale HUC polygon. This procedure looked for both new or missing polygons, and was also used to check attribute values. I also dissolved both coverages by accounting unit and compared the number and location of remaining polygons.
Problems with labels/attributes:
(1) I discovered a total of 649 places where the HUC codes from the label point of the 1:2,000,000 coverage did not match the HUC code for the 1:250,000 HUC polygon that it fell within. As you had indicated in the documentation, there were a lot of differences in California. The 2m HUC had lots of label points resulting from islands, bays, and estuaries that are not included in the 1:250,000 scale HUC coverages. In other places the polygons seemed to be the same but the HUC codes were different. For example HUC 18020111 in the 1:2,000,000 coverage is coded as HUC 18020023 in the 1:250,000 coverage. There were also many differences in the Great Lakes. It seems odd that the 1:2,000,000 coverage should have more detail with regard to coastal features than the 1:250,000 scale coverage has. There were also internal polygon label differences in Minnesota (7100001 in 250k, 70200001 in 2m), Colorado (10090204 in 250k, 10180007 in 2m), Illinois (mistake in the 2m HUC I think), and Louisiana (11140203 in 250k, 11140202 in 2m). Texas and Florida also have a few that look like they should be checked.
(2) The dissolved 1:2,000,000 coverage contained 350 accounting unit polygons while the dissolved 1:250,000 HUC coverage only contained 177. There were large differences in the way the Accounting unit polygons looked in the Great Lakes Region, and in parts of California, Wyoming, and Florida. Again, many of the differences result from the use of a cruder coastline in the 1:250,000 scale HUC coverage.
Coverage Documentation:
The coverage documentation was reviewed both editorially and for overall completeness. The documentation was editorially sound and did not need any corrections.
Problems with the Documentation:
(1) The redefined items in the pat file were not defined in the data dictionary portion of the documentation file.
(2) The complete reference to the source material for the data is not in the documentation file."
Response to Peer review by Bill Battaglin, 1/5/93, Doug Nebert,USGS-WRD Reston ----------------------------------------------------------------------
Data were reviewed for attribute accuracy against a 1:2million base through random audit of polygon features. Line attributes were verified by symbol- ization on the screen. Regions were shaded in to verify correct polygon values for HUC at the Hydrologic Region level. Documentation was updated. The short arcs along the quadrangle boundaries were kept in the data set due to the importance of maintaining as much original information as possible. Basin codes were updated and additional erroneous neatlines removed.
Peer review, 11/10/93, Doug Nebert, USGS-WRD, Reston, memo to Paul Kapinos: --------------------------------------------------------------------------- "As you are aware, we have several digital versions of the hydrologic unit maps for the United States and I am in the process of verifying and publishi a 1:250,000-scale version derived from National Mapping Division Geographic Information Retrieval and Analysis System (GIRAS) data as part of their land use mapping program of the 1970s and early 1980s.
In comparing the 1:250,000-scale data reviewers noticed differences in both basin definition and hydrologic unit codes in Southern California and in the San Joaquin valley. The 1974 state map, at 1:500,000-scale agrees with the 1:250,000-scale GIRAS data in boundaries and numbers, whereas the 1:2.5 mill "wall map" of the U.S. agrees with the 1:2,000,000 digital data set. Both p maps are authoritative sources of information, but apparently something chan between the two maps.
On a related note, it is worthwhile to mention that the 1:2.5 million-scale wall map for the western U.S. is being revised to include new Alaska hydrolo unit codes before reprinting. It would be wise to be sure that the boundari depicted there are also the authoritative ones.
I would appreciate your review and adjudication of the California hydrologic unit definitions in order for us to publish this digital data set. Please provide a written response (e-mail and paper copy) and marked-up maps as to which basins and boundaries are current."
Peer review, 11/29/93, Paul Kapinos, USGS-WRD, memo to Doug Nebert: ------------------------------------------------------------------- "The discrepancies in the hydrologic unit codes (and some boundaries) in the State of California are due to the fact that the California State Hydrologic Unit Map (HUM) was revised in 1978 but the 1:250,000-scale digital data set was not. The events that most likely occurred can be summarized as follows:
o The 1:500,000-scale HUMs were published by OWDC over a period of about four years between 1974 and 1978.
o The National Mapping Division (NMD) overlaid the hydrologic unit boundaries on their 1:250,000-scale land-use and land-cover map series after each State HUM was completed, and later digitized these boundaries and their respective codes.
o In 1978, the State of California asked OWDC to revise the hydrologic unit boundaries and codes in the central valley.
o The 1:500,000-scale California HUM was revised and reprinted but NMD was either not informed of the revisions or chose not to revise or redigitize their 1:250,000-scale overlays.
o Once all the HUMs were printed (including the 1978 revisions of California and South Dakota), the 1980 1:2.5 million-scale United States wall map was published using the up-to-date (1978) boundaries and codes.
Based on the above summary, I would recommend using the boundaries and codes from the 1:2.5 million-scale map and the 1:2,000,000 digital data set. Please be aware that other hydrologic unit boundaries and/or codes may have been revised when individual State HUMs were reprinted by OWDC. I doubt if there has been any attempt to update any of the digital data sets with these changes."
Response to Peer Review by Paul Kapinos, Doug Nebert 2/14/94: -------------------------------------------------------------
The areas in question in California were updated to reflect the more current information as contained in the 1:2 million data set. Polygon hydrologic unit codes were updated in the Central Valley and in coastal Southern California. Where necessary, 1:2 million-scale linework was substituted to define the correct basin boundaries where no corresponding information was available at a different scale.
Related_Spatial_and_Tabular_Data_Sets: Any data set which has hydrologic unit codes as part of their data may be able to use this data.
Other_References_Cited:
U.S. Geological Survey, 1990. Land Use and Land Cover Digital Data from 1:250,000- and 1:100,000-Scale Maps. Data Users Guide 4, 33 pp, Reston Virginia.
Notes:
Continually Daily Weekly Monthly Annually Unknown As Needed Irregular None planned
The SOURCE item has four special codes to describe the source linework. Code 1 stands for all arcs that were from 1:100,000 scale GIRAS files and were internal to the quadrangle (no neatlines). Code 2 stands for all arcs from the 1:250,000-scale GIRAS files which were internal to the quadrangle. Code 3 is for lines from either GIRAS source scale but were part of the neatline which may be used to connect arcs that don't join cleanly between quads. Code 4 is for linework in the southern Central Valley and southern Coastal California where the GIRAS data were replaced with 1:2 million scale basin boundaries.
A companion NAMES file (HUC250.NAMES) is provided with this data set to allow a user to perform a temporary join between the basin polygons and display or query basins based on their assigned text names rather than just the basin number (HUC).