DRG (Digital Raster Graphic)
Mar 7,2026

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Introduction

DRG (Digital Raster Graphic) is a raster data format created by scanning paper topographic maps at high resolution and adding georeferencing information. Primarily produced by the United States Geological Survey (USGS) through digitization of topographic maps, it preserves map information such as contour lines, roads, hydrography, and administrative boundaries as images. Since DRG contains geographic coordinate information, it can be overlaid with other geographic data in GIS and is widely used as base maps or reference maps.

File Structure

A DRG dataset typically consists of the following elements:

Raster image file (usually GeoTIFF format): Stores the scanned topographic map image itself. It is often saved in TIFF format with embedded georeferencing information.
World file (e.g., .tfw): Records geometric transformation information such as pixel size, rotation, and upper-left coordinates, used to place the image in the correct position.
Projection information file (.prj): Defines the coordinate system, such as UTM or state plane coordinate systems.
Metadata file: Includes supplementary information such as creation year, scale, sheet boundaries, and data source.

Pros

Digital utilization of existing paper maps: Traditional paper topographic maps can be used directly in digital environments, allowing historical map information to be integrated into GIS.
High visibility: Contour lines, annotations, and map symbols are displayed as-is, making visual understanding easy.
Georeferencing support: With coordinate information attached, they can be overlaid with other vector or raster data.
Standard image format storage: Often provided in GeoTIFF format, making them readable by various GIS software.
Value as historical materials: Useful for comparative analysis of past terrain conditions and land use.

Cons

No vector information included: Roads and contour lines are stored as images, preventing direct attribute searches or edits.
Large data capacity: Due to high-resolution scanning, file sizes can be relatively large.
Low updateability: Dependent on original paper maps, making updates with the latest information difficult.
Unsuitable for analytical purposes: As image data, they are not suitable for advanced spatial analysis such as elevation analysis or network analysis.
Impact of projection/correction errors: Slight positional errors may occur depending on the accuracy of scanning and georeferencing processing.

Application Scenario

DRG is suitable for use as base maps or reference maps for historical maps, serving as foundational materials in urban planning and environmental surveys. By overlaying with existing vector data, it is effective for visually confirming topographical relationships and feature positions. It is also widely used for comparing past and present terrain changes, analyzing land use transitions, and educational purposes. In GIS environments, it can be considered a raster data format more suitable for reference and display purposes than for precise analysis.