GIS Data Catalog

The database was moved from individual township-range grids to a seamless SDE GDB raster mosaic at 2-foot resolution.

This was part of the process of migrating large raster databases to the SDE environment so that any updates could be made to the entire database and then subset products, such as the township-tiled grids, could be extracted from the master.

The schema of the SDE GDB raster mosaic was updated.

The original schema contained a single item VALUE which encoded one of three domain values: 1 = high confidence impervious surface, 2 = lower confidence impervious surface, and 5 = added from the transportation network layers (early version of TRANS_NETWORK).

As part of the plan to update the 2000 impervious surface product to a 2007 product, the schema was modified so that the VALUE field encodes an integer that reflects the data source: 1.

Value = 1 indicates impervious surface comes from 2000 DAIS imagery 2.

Value = 2 indicates impervious surface comes from 2000 Emerge imagery 3.

Value = 3 indicates impervious surface comes from 2001 Ikonos imagery 4.

Value = 4 indicates impervious surface comes from 2000 TRANS_NETWORK geometry.

An additional item IMP was added and encoded to 1 so that all cells, regardless of source, are indicated as impervious.

This also makes it possible to symbolize the grid by a single impervious value.

The reg_imp shapefile, derived from the reg_imp030 grid, had drawing errors when used in ArcMap.The layer would display all feature polygons when zoomed out to large extents, but failed to draw all polygons when zoomed in.

This was likely due to the large, contiguous polygons of impervious (GRID_CODE = 1) that extended well beyond the draw window.

To break up these large polygons, the shapefile was converted (SHAPE2POLY) to a coverage and then UNIONED with a coverage version of IDXPTRMID, the township-range tiling index.

The resulting union created intersect lines where a township boundary occurred, thus breaking up the large polygons.

Although this created intersect lines in the overall layer, it now displays properly in ArcMap.

The SHAPE2POLY and UNION actions also added several auto-generated attributes as well as the user attributes from the IDXPTRMID coverage.

The unnecessary auto-attributes were dropped so as to match the original schema of the REG_IMP.SHP shapefile.

However the user attributes describing the township and range locations were left in the attribute table to allow query and selection by township-range, if necessary.

During GIS application use of the dataset, the following quality issues were noted and addressed as indicated: 1.

Some shapefiles contained attribute (item) names that were not consistent across all files.

A python script was used to query all shapefile table objects to identify the item inconsistency.

As the grid-code item is the only required field for the data all fields after the system-defined and before grid-code were dropped from the shapefiles.

This was more effective than renaming the items and reduced the file size.

2.

T25R06 grid tile did not cover the full extent of that tiles MBR.

The subject township and all adjacent townships were merged and clipped to the correct MBR.

The grid was processed through to shapefile using the same process steps as described in the original process stanzas 3.

Projection headers of some of Grid tiles was incorrect The grid headers were updated using the ArcGIS Workstation commandline Projectdefine command with the following parameters.

Projection Stateplane Zone 5601 Datum HPGN Units FEET Spheroid GRS1980 This corrected the erroneously defined zone of 5610 and 5106.

All grids and shapefiles were reinspected for correct extent, attribution and attribute values.

Prepared grids were imported into ERDAS as img files.

Split screen arrangement was used to display visible version of source imagery along side the classified grid.

Several editors were employed.

One lead editor was used to instruct other editors to maintain as great as consistency between tiles as possible.

The main purpose of the editing was to remove gross commission errors.

Based on interpretation of the associated imagery areas of commission were outlined as Areas of Interest (AOI) and recoded as non-impervious (i.e., set to NULL).

General guidelines and observations used in editing: 1.

Most areas of heavy forest appeared as impervious and were recoded.

2.

Rivers and streams also appeared as impervious and were recoded.

3.

Bare earth and fallow agricultural fields show mixed to full impervious and were recoded.

4.

Areas of obvious construction were not recoded.

Ancillary imagery was sometimes employed to reconcile ambiguous situations.

If area still remained ambiguous and could not be edited per rules, then 50% of area was recoded.

In areas of dense urbanization, this recoding average would be reduced, leaving more of the area as impervious.

Large bodies of water had previously been removed by the vendor employing a coincident Landsat TM interpretation.

This coarse editing technique errored towards not clipping the water/shore boundary but in some instances this could not be avoided.

Again not omission correction was applied.

In areas water/shore areas where additional editing was done, wooden/floating docks were removed.

However, permanent docks/piers were not recoded.

Other areas of omission error, shadowed or shade-covered impervious features, (e.g., features in shadow of tall building) were not corrected.

After editing was completed in Erdas, ArcView 3.x spatial analyst was used to convert the img file back to an ArcInfo grid.

This grid was then processed to convert any zero values (as recoded in Erdas) to NULLs so that the only valid values left in the grid would be 1, 2, and 5.

Projection header was defined per King County standards and grid was posted to Spatial Data Warehouse.

Copy of the grid was remapped to new grid collapsing all non-null values to a value of 1, representing impervious/impacted surface regardless of original coded value.

Grid converted to polygon file using GRIDPOLY command.

Polygon coverage converted to shapefile using SHAPEARC command with Polygon argument ArcView used to display and quality assess the shapefile interpretation and the original grid together.

Shapefile reselected for grid-code <> -9999 to remove all null islands created during the GRIDPOLY conversion.

Reselect shapefile moved to Spatial Data Warehouse, projection file added, and final inspection made.

Grid data delivered by vendor was mosaiced from original tiles.

Data was retiled into township-range tiling scheme.

Best-available road network database was buffered to 15-feet and merged to grid tiles.

Conditional statement was used so that road value (id =5) was added only where there was a null or zero grid value.

For Vashon Island see process document "<https://www5.kingcounty.gov/sdc/raster/landcover/DAIS_Process_doc.htm>" For western King County see process document "<https://www5.kingcounty.gov/sdc/raster/landcover/Emerge_Process_doc.htm>" For eastern King County see process document "<https://www5.kingcounty.gov/sdc/raster/landcover/Ikonos_Process_doc.htm>"

External city shapefile data was added with new source Values: Value 1, Vashon Island was interpreted from 4-band, 12-bit rgb-infrared, 1.64 meter ground sample distance (gsd) data. Value 2, Western King County and southwestern Snohomish County from Range 03 to Range 07 was interpreted from 3-band, 8-bit rg-infrared, 2 foot gsd data. Value 3, Eastern King County from Range 08 to Range 11 was interpreted from 4-band, 16-bit, rgb-infrared 4-meter data. Value 4, King County T-Net dated 2000

Erased errors in following townships: T28R04 T28R05 T27R03 T27R04 T27R05 T27R06 T26R03 T26R04 T26R13 T25R03 T25R13 T24R11 T21R02 T19R11