Digital line graphs from 1:24,000-scale maps

The discipline of cartography is undergoing a number of profound changes that center on the emerging influence of digital manipulation and analysis of data for the preparation of cartographic materials and for use in geographic information systems. Operational requirements have led to the development by the USGS National Mapping Division of several documents that establish in-house digital cartographic standards. In an effort to fulfill lead agency requirements for promulgation of Federal standards in the earth sciences, the documents have been edited and assembled with explanatory text into a USGS Circular. This Circular describes some of the pertinent issues relative to digital cartographic data standards, documents the digital cartographic data standards currently in use within the USGS, and details the efforts of the USGS related to the definition of national digital cartographic data standards. It consists of several chapters; the first is a general overview, and each succeeding chapter is made up from documents that establish in-house standards for one of the various types of digital cartographic data currently produced. This chapter, 895-C, describes the data format and structure together with current attribute codes used for digitizing USGS 1:24,000-scale maps. INTRODUCTION This document describes the digital line graphs (DLG's) prepared from the 7.5-minute, and in some cases 15-minute, materials associated with the USGS Topographic Map Series. The series will eventually provide complete national coverage. The data are collected from 7.5-minute source materials at 1:24,000 or 1:25,000 scale where possible; when 7.5-minute sources are not available, 15minute sources at 1:48,000 or 1:62,500 scale are used. The digital data are useful for the production of cartographic products, such as base maps, and the data are structured to support the analytical functions of geographic information systems. A typical use of base category digital cartographic data is to combine them with other geographically referenced data, enabling various automated spatial analyses to be conducted.