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Digital Base Maps

Pennsylvania’s geologic maps show rock units and other geologic data with respect to their position in our state.

Base layers -- such as roads, topography, and streams -- provide the references that individuals use to identify locations.

Today, many base map layers are created from digital data. The Pennsylvania Geological Survey lists sources of digital base map data on their published map plates.

Much of this data comes from the Pennsylvania Spatial Data Access and The National Map websites.

Start With Lidar

Lidar is an acronym for “light detection and ranging” and refers to a remote-sensing technique used to collect high-resolution elevation data.

From this data, scientists construct detailed models of the earth’s surface as well as objects on the surface, such as:

  • Buildings
  • Trees
  • Low-level vegetation
  • Utility lines

Lidar data can be processed to produce a variety of layers, including:

  • Height of tree canopies
  • Building locations and height
  • Bare-earth digital elevation models
  • Topographic contours

When vegetation and other raised objects are stripped away through data processing, digital elevation models can reveal “hidden” features such as landslide scars and archaeological sites.

The Pennsylvania Geological Survey uses digital elevation models to produce hillshades (shaded-relief images) that provide a key base layer for its geologic maps.

As the value of lidar data is being realized, the quality of this data is increasing.

Pick Quality

The PAMAP Program, which was administered by the Pennsylvania Geological Survey in partnership with other government agencies, collected statewide Quality Level 3 lidar data from 2006 - 2008.

Now, the U.S. Geological Survey (USGS) National Geospatial Program and other agencies have collected Quality Level 2 lidar elevation data for the entire state.

The minimum cell size of Quality Level 3 data is 2 meters, and the minimum cell size of Quality Level 2 data is 1 meter -- therefore, the resolution of available lidar will be improved considerably.

The 2015 USGS fact sheet 3D Elevation Program -- Summary for Pennsylvania  (PDF) indicates that Quality Level 2 lidar data have expected benefits of $7.5 million annually for Pennsylvania.

The top 10 business uses it lists for lidar are relevant to the work performed by DCNR and other state agencies:

  • Natural resources conservation
  • Agriculture and precision farming
  • Flood risk management
  • Infrastructure and construction management
  • Water supply and quality
  • Forest resources management
  • Aviation navigation and safety
  • Geologic resource assessment and hazard mitigation
  • Coastal zone management
  • Renewable energy resources

Add Water

The shape of the land greatly determines the locations and pathways of Pennsylvania’s water -- its lakes, rivers, and streams.

The Pennsylvania Geological Survey is using the new Quality Level 2 lidar elevation data to compile the Pennsylvania Hydrography Dataset.

This will be a dynamic, statewide dataset that is scale equivalent to the most currently available elevation data.

As new lidar is flown, ​ the Pa. Hydrography Dataset will be updated to reflect spatial and temporal changes that include improved resolution.

Another primary source of digital water features has been the USGS National Hydrography Dataset -- a nationwide, vector representation of drainage networks derived from published USGS topographic quadrangle maps and U.S. Forest Service Primary Base Series maps.

While the National Hydrography Dataset has a recommended-use scale of 1:24,000, the Pa. Hydrography Dataset is accurate to a 1:2,400 scale -- meaning its “flowpaths” show greater detail.

And because the lidar elevation data used to derive the hydrography are recent, the flowpaths more accurately reflect today’s landscape.

The Pa. Hydrography Dataset is a work in progress, and various methodologies are being studied.

The Pennsylvania Geological Survey's Progress Report 21–01.0, Pennsylvania Hydrography Dataset -- The Pennsylvania Geological Survey’s Process for Generating Flowpaths (PDF), documents the current workflow.

DCNR encourages people involved in this type of data generation to test the outlined workflow for themselves. You can help by:

  • Suggesting improvements to the process -- particularly with regards to automation. The most significant detriment to the current workflow is the time and manual labor it requires

  • Creating and submitting your own data

If you have input or questions about the Pa. Hydrography Dataset process or data, email DCNR’s Bureau of Geological Survey.

As of August 2021, the Pennsylvania Geological Survey has packaged and released hydrography data for 13 local watershed areas.

These datasets can be downloaded from the Pennsylvania Spatial Data Access website. Other watershed datasets will be added as they are produced.

Finish With Other Data

Other base map digital data may include such items as:

  • Topographic (elevation) contours
  • Towns
  • Roads
  • Political boundaries

These data are available from several sources.

The National Map

The National Map Download web page allows searches for a variety of vector data (including the aforementioned National Hydrography Dataset) by area.

DCNR staff often will utilize the Topo Map and Topo Stylesheet data to create subdued, readable base maps when working on a 7.5-minute quadrangle geologic map.

Pa. Spatial Data Access

The Pennsylvania Spatial Data Access website allows searches by keywords, data provider, theme, or county.

The Apps & Tools web page has various map applications structured specifically for previewing and downloading lidar data products and orthoimagery.