Geological map


A geological map or geologic map is a special-purpose map made to show various geological features. Rock units or geologic strata are shown by color or symbols. Bedding planes and structural features such as faults, folds, are shown with strike and dip or trend and plunge symbols which give three-dimensional orientations features. Geological mapping is an interpretive process involving multiple types of information, from analytical data to personal observation, all synthesized and recorded by the geologist. Geologic observations have traditionally been recorded on paper, whether on standardized note cards, in a notebook, or on a map.
Stratigraphic contour lines may be used to illustrate the surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units. It is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed.
Digital geological mapping is the process by which geological features are observed, analyzed, and recorded in the field and displayed in real-time on a computer or personal digital assistant. The primary function of this technology is to produce spatially referenced geological maps that can be utilized and updated while conducting field work.

Symbols

Lithologies

Rock units are typically represented by colors. Instead of colors, certain symbols can be used. Different geological mapping agencies and authorities have different standards for the colors and symbols to be used for rocks of differing types and ages.

Orientations

Geologists take two major types of orientation measurements : orientations of planes and orientations of lines. Orientations of planes are measured as a "strike" and "dip", while orientations of lines are measured as a "trend" and "plunge".
Strike and dip symbols consist of a long "strike" line, which is perpendicular to the direction of greatest slope along the surface of the bed, and a shorter "dip" line on side of the strike line where the bed is going downwards. The angle that the bed makes with the horizontal, along the dip direction, is written next to the dip line. In the azimuthal system, strike and dip are often given as "strike/dip".
Trend and plunge are used for linear features, and their symbol is a single arrow on the map. The arrow is oriented in the downgoing direction of the linear feature and at the end of the arrow, the number of degrees that the feature lies below the horizontal is noted. Trend and plunge are often notated as PLUNGE → TREND.

History

The oldest preserved geological map is the Turin papyrus, which shows the location of building stone and gold deposits in Egypt.
The earliest geological map of the modern era is the 1771 "Map of Part of Auvergne, or figures of, The Current of Lava in which Prisms, Balls, Etc. are Made from Basalt. To be used with Mr. Demarest's theories of this hard basalt. Engraved by Messr. Pasumot and Daily, Geological Engineers of the King." This map is based on Nicolas Desmarest's 1768 detailed study of the geology and eruptive history of the Auvergne volcanoes and a comparison with the columns of the Giant's Causeway of Ireland. He identified both landmarks as features of extinct volcanoes. The 1768 report was incorporated in the 1771 Royal Academy of Science compendium.
The first geological map of the U.S. was produced in 1809 by William Maclure. In 1807, Maclure undertook the self-imposed task of making a geological survey of the United States. He traversed and mapped nearly every state in the Union. During the rigorous two-year period of his survey, he crossed and recrossed the Allegheny Mountains some 50 times. Maclure's map shows the distribution of five classes of rock in what are now only the eastern states of the present-day US.
The first geological map of Great Britain was created by William Smith in 1815 using principles first formulated by Smith.

Software history

Mapping in the digital era

In the 21st century, computer technology and software are becoming portable and powerful enough to take on some of the more mundane tasks a geologist must perform in the field, such as precisely locating oneself with a GPS unit, displaying multiple images, plotting strike and dip symbols, and color-coding different physical characteristics of a lithology or contact type between rock strata. Additionally, computers can now perform some tasks that were difficult to accomplish in the field, for example, handwriting or voice recognition and annotating photographs on the spot.
Digital mapping has positive and negative effects on the mapping process; only an assessment of its impact on a geological mapping project as a whole shows whether it provides a net benefit. With the use of computers in the field, the recording of observations and basic data management changes dramatically. The use of digital mapping also affects when data analysis occurs in the mapping process, but does not greatly affect the process itself.

Advantages

  • Data entered by a geologist may have fewer errors than data transcribed by a data entry clerk.
  • Data entry by geologists in the field may take less total time than subsequent data entry in the office, potentially reducing the overall time needed to complete a project.
  • The spatial extent of real world objects and their attributes can be entered directly into a database with geographic information system capability. Features can be automatically color-coded and symbolized based on set criteria.
  • Multiple maps and imagery can easily be carried and displayed on-screen.
  • Geologists may upload each other's data files for the next day's field work as reference.
  • Data analysis may start immediately after returning from the field, since the database has already been populated.
  • Data can be constrained by dictionaries and dropdown menus to ensure that data are recorded systematically and that mandatory data are not forgotten
  • Labour-saving tools and functionality can be provided in the field e.g. structure contours on the fly, and 3D visualisation
  • Systems can be wirelessly connected to other digital field equipment

    Disadvantages

  • Computers and related items must be carried in the field.
  • Field data entry into the computer may take longer than physically writing on paper, possibly resulting in longer field programs.
  • Data entered by multiple geologists may contain more inconsistencies than data entered by one person, making the database more difficult to query.
  • Written descriptions convey to the reader detailed information through imagery that may not be communicated by the same data in parsed format.
  • Geologists may be inclined to shorten text descriptions because they are difficult to enter, resulting in loss of data.
  • There are no original, hardcopy field maps or notes to archive. Paper is a more stable medium than digital format.

    Educational and scientific uses

Some universities and secondary educators are integrating digital geological mapping into class work. For example, The GeoPad project describes the combination of technology, teaching field geology, and geological mapping in programs such as Bowling Green State University’s geology field camp.
At Urbino University :it:Università di Urbino, Field Digital Mapping Techniques are integrated in Earth and Environmental Sciences courses since 2006 .
The MapTeach program is designed to provide hands-on digital mapping for middle and high school students. The SPLINT project in the UK is using the BGS field mapping system as part of their teaching curriculum
Digital mapping technology can be applied to traditional geological mapping, reconnaissance mapping, and surveying of geologic features. At international digital field data capture meetings, major geological surveys discuss how to harness and develop the technology. Many other geological surveys and private companies are also designing systems to conduct scientific and applied geological mapping of, for example, geothermal springs and mine sites.

Equipment

The initial cost of digital geologic computing and supporting equipment may be significant. In addition, equipment and software must be replaced occasionally due to damage, loss, and obsolescence. Products moving through the market are quickly discontinued as technology and consumer interests evolve. A product that works well for digital mapping may not be available for purchase the following year; however, testing multiple brands and generations of equipment and software is prohibitively expensive.

Common essential features

Some features of digital mapping equipment are common to both survey or reconnaissance mapping and “traditional” comprehensive mapping. The capture of less data-intensive reconnaissance mapping or survey data in the field can be accomplished by less robust databases and GIS programs, and hardware with a smaller screen size.
  • Devices and software are intuitive to learn and easy to use
  • Rugged, as typically defined by military standards and ingress protection ratings
  • Waterproof
  • Screen is easy to read in bright sunlight and on gray sky days
  • Removable static memory cards can be used to back up data
  • Memory on board is recoverable
  • Real-time and post-processing differential correction for GPS locations
  • Portable battery with at least 9 hours of life at near constant use
  • Can change batteries in the field
  • Batteries should have no “memory,” such as with NiCd
  • Chargeable by unconventional power sources
  • Wireless real-time link to GPS or built-in GPS
  • Wireless real-time link from computer to camera and other peripherals
  • USB port

    Features essential to capture traditional geologic observations

Hardware and software only recently became available that can satisfy most of the criteria necessary for digitally capturing "traditional" mapping data.
  • Screen about —compact but large enough to see map features. In 2009, some traditional mapping is conducted on PDAs.
  • Lightweight—ideally less than 3 lbs.
  • Transcription to digital text from handwriting and voice recognition.
  • Can store paragraphs of data.
  • Can store complex relational database with drop-down lists.
  • Operating system and hardware are compatible with a robust GIS program.
  • At least 512 MB memory.