This data set is not, and was not meant to be, an exclusive index to USGS 7.5' map products and their spatial footprint. There are several reasons for this:
The data set does not represent the exact footprint of 7.5' paper map and DRG products because most of those products were based on a regular 7.5 minute geographic grid relative to the NAD27 datum. Because of an approximate 25 meter coordinate shift between the two datums, the physical area covered by each cell of this grid (under its NAD83 definition) is slightly different from the physical area covered by most corresponding 7.5' paper maps or DRGs.
Six 7.5' USGS quadrangle maps covering the Chandeleur Islands were offset from the normal basepoints for 7.5' maps in order to cover the area with the fewest number of maps. This dataset does not capture that offset because it is totally regular, however each of the Chandeleur Islands cells has an attribute to indicate that the corresponding USGS 7.5' map was offset.
This dataset includes cells that do not have a corresponding USGS 7.5' map name. Those cells are named is this data set so the corresponding child orthophotos can also have a name, rather than a purely numeric identifier.
quad24k.mtd - this metadata in mp (metadata parser) compatible ASCII text form quad24k.html - this metadata in HTML form quad24k_faq.html - this metadata presented as Questions and Answers quad24k.sgml - this metadata in SGML form quad24k1.gif - thumbnail graphic of data set
If these data are altered or incorporated into another dataset, they are not to be redistributed without also: altering the name of the dataset, including a Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998) compliant metadata file that describes the dataset and reflects the alteration steps that makes the new dataset different from this one, and citing this dataset in the metadata as a source for the altered dataset using the source citation specified below.
If these digital data are used in the production of a report or in the compilation of a standalone printed map, then this dataset is to be cited in the report or on the map using the source citation specified below.
The following source citation is to be used when citing this dataset: LOSCO Environmental Baseline Inventory Dataset '24K (7.5') Grid Index for Louisiana, Geographic NAD83, LOSCO (1999) [quad24k]'
Users hereby agree to abide by the use and reproduction conditions specified above. By using the data described in these metadata, the user acknowledges that the terms and conditions of use have been read and that the user is bound by these criteria.
This code is identical to the usgs_no value, however this attribute gives codes for cells that have no corresponding USGS map.
These data have been developed from the best available sources. Although efforts have been made to ensure that the data are accurate and reliable, errors and variable conditions originating from physical sources used to develop the data may be reflected in the data supplied. Users must be aware of these conditions and bear responsibility for the appropriate use of the information with respect to possible errors, scale, resolution, rectification, positional accuracy, development methodology, time period, environmental and climatic conditions and other circumstances specific to these data. The user is responsible for understanding the accuracy limitations of the data provided herein. The burden for determining fitness for use lies entirely with the user. The user should refer to the accompanying metadata notes for a description of the data and data development procedures.
Although these data have been processed successfully on computers at the LOSCO, no guarantee, expressed or implied, is made by LOSCO regarding the use of these data on any other system, nor does the act of distribution constitute or imply any such warranty. Distribution of these data is intended for information purposes and should not be considered authoritative for navigational, engineering, legal and other site-specific uses.