Understanding KCGIS Raster Data

Structure, Naming Conventions, Metadata

Introduction
Tiling scheme
File structure
Decoding the file names
    The "Tile"section
    The "Data set" section
Other files (indexes, etc.)

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Introduction

What this document is/is not: This document can be considered a "quick start" reference guide to KCGIS raster data, meant to aid the occasional user in finding and loading the data. It is not a comprehensive listing of KCGIS raster holdings, their types, origins, or metadata.

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Tiling Scheme

The raster data have four levels of tiling available, with various levels of resampling or compression. Not all raster sets will be represented by all four levels.

"Idxp" stands for "index polygons," which is the definition of the tiling scheme.

Idxp7500: "Building block tiles" are 7500 feet per side, and are the highest resolution available. Intended primarily for storage and maintenance, not project use; however, may be useful for detailed analysis of a very small area. View a graphic.

Idxptrmbr: "Township Range Minimum Boundary Rectangle." Tiles correspond roughly to a single township-range block. Primary access for users, most of these datasets have the same resolution at this level as their corresponding idxp7500 tiles. View a graphic.

Idxpzone: Geographic zones, each of which encompasses about 20 idxptrmbr tiles. Most useful for large-area analysis. View a graphic.

KeyRegion: Technically not tiled, this level consists of a single compressed file that covers the entire extent of the given raster data set. Compression algorithm varies by dataset with a corresponding impact on resolution quality. View a graphic.

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File Structure

Raster data is housed on /plibrary3, and is stored by tile level.

Idxp7500 and idxptrmbr data are grouped into data sets.

Examples:

• ortho_2000emerge"
• "dgm_hillshade"
• .....

Idxpzone data are grouped into four geographic areas (NW, NE, SW, SE)

Keyregion files contain data for a given theme in a single file. Four subdirectories organize the data into major data groups:

• Orthoimagery: High-resolution digital aerial photography and moderate-resolution satellite imagery
• Otherimagery: Digital USGS topographic images, lower-resolution satellite imagery
• Elevation: Lidar-derived topographic data, and lower resolution USGS Digital Elevation Models
• Landcover: Landcover interpretations derived from multispectral satellite imagery, and higher-resolution impervious surface analysis

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Decoding the file names

Each file name can be broken into two parts, separated by an underscore. The first part defines the tile, and the second defines the data set.

Tiles:

Idxp7500:
Four characters in the form of <row><column>.
Example: "ak27_..."

Idxptrmbr:
Six characters in the form t<township>r<range>.
Example: "t22r12_..." represents Township 22, Range 12.

Idxpzone:
Three characters: z<zone>. There are only four:

• znw: Northwest Zone
• zne: Northeast Zone
• zsw: Southwest Zone
• zse: Southeast Zone

Keyregion:
All begin with reg

Data Sets:

Non-Image data (lidar, hillshade, tins, etc.):
Three- to six-character descriptive code.

Image data:
The first two characters represent the year of acquisition.
Example: t22r07_02n100.

The third character identifies the image type (band combination)
Example: t22r07_02n100:

• c = color infrared imagery
• m = multispectral and hyperspectral imagery
• n = natural color imagery
• p = panchromatic (b&w) imagery
• r = pan-sharpened imagery
• s = satellite imagery (Landsat, SPOT, TM, etc.)

The last set of characters for image data defines the resolution of the data.

Orthophoto images: Three digits that represent pixel resolution in hundredths of a foot, eg., t22r07_02n100
Examples:

• 1-foot pixel resolution: 100
• 0.5-foot pixel resolution: 050
• 6-foot pixel resolution: 600
• 0.5-meter pixel resolution: 164 (0.5m is approx. 1.64 ft)

Other raster/cell based (non-photo) data: Three digits that represent the resolution in feet, eg, t22r07_dgm006.
Examples:

• 6-foot lodar digital elevation data: 006
• 26-meter NED: 086 (26 m converted to nearest State Plane integer is 86)

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Other files (indexes, etc)
Other related files are found in /plibrary3/reference.

Indexes
Contains indexes for idxp7500, idxptrmbr, and idxpzone.

Extents:
Contains individual shapefiles representing the acutal useable data extent for each enterprise data set.

Naming convention: x_<descriptor>, where descriptor is the same as the "data set" descriptors described above.

This folder also contains:

• Allextents.shp - a merged combination of all the individual files joined to an attribute table briefly describing each data set. This file includes the extent for all enterprise landcover, orthoimagery, lidar data and satellite imagery.
• Imageextentsall.shp - a single shapefile which displays the extent, and additional descriptive metadata, for all orthoimagery and satellite imagery data sets.

Status:
Contains several shapefiles that track the inventory of raster tiles. Most useful: raststat_trmbr - a current record of all township-range tiles by data set item, and raststat_7500 - a record of all 7500 tiles by dataset item.