Geological map

Lithologies

Rock units are typically represented by colors. Instead of (or in addition to) 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 (using a hand compass, for example a Brunton compass): 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" (for example: 270/15, for a strike of west and a dip of 15 degrees below the horizontal).

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 (the "trend") and at the end of the arrow, the number of degrees that the feature lies below the horizontal (the "plunge") is noted. Trend and plunge are often notated as PLUNGE → TREND (for example: 34 → 86 indicates a feature that is angled at 34 degrees below the horizontal at an angle that is just east of true south).

Software history

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 (GIS) capability. Features can be automatically color-coded and symbolized based on set criteria.
• Multiple maps and imagery (geophysical maps, satellite images, orthophotos, etc.) 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 (such as digital cameras and sensor webs)

Disadvantages

• Computers and related items (extra batteries, stylus, cameras, etc.) 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 (either by handwriting or voice recognition), 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.^[27]

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.^{[31] [12]}

• Devices and software are intuitive to learn and easy to use
• Rugged, as typically defined by military standards (MIL-STD-810) 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 (generators, solar, etc.)
• Wireless real-time link to GPS or built-in GPS
• Wireless real-time link from computer to camera and other peripherals
• USB port(s)

Features essential to capture traditional geologic observations

Hardware and software only recently (in 2000) became available that can satisfy most of the criteria necessary for digitally capturing "traditional" mapping data.

• Screen about 5 in × 7 in (130 mm × 180 mm)—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 (text fields).
• 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.

Software

Since every geological mapping project covers an area with unique lithologies and complexities, and every geologist has a unique style of mapping, no software is perfect for digital geological mapping out of the box. The geologist can choose to either modify their mapping style to the available software, or modify the software to their mapping style, which may require extensive programming. As of 2009^[update], available geological mapping software requires some degree of customization for a given geological mapping project. Some digital-mapping geologists/programmers have chosen to highly customize or extend ESRI's ArcGIS instead. At digital field data capture meetings such as at the British Geological Survey in 2002 some organisations agreed to share development experiences, and some software systems are now available to download for free.

Singapore

The first geological map of Singapore was produced in 1974, produced by the then Public Work Department. The publication includes a locality map, 8 map sheets detailing the topography and geological units, and a sheet containing cross sections of the island.

Since 1974, for 30 years, there were many findings reported in various technical conferences on newfound geology islandwide, but no new publication was produced. In 2006, Defence Science & Technology Agency, with their developments in underground space promptly started a re-publication of the Geology of Singapore, second edition. The new edition that was published in 2009, contains a 1:75,000 geology map of the island, 6 maps (1:25,000) containing topography, street directory and geology, a sheet of cross section and a locality map.

The difference found between the 1976 Geology of Singapore report include numerous formations found in literature between 1976 and 2009. These include the Fort Canning Boulder Beds and stretches of limestone.

United Kingdom

The United Kingdom and Isle of Man have been extensively mapped by the British Geological Survey (BGS) since 1835; a separate Geological Survey of Northern Ireland (drawing on BGS staff) has operated since 1947.

Two 1:625,000 scale maps cover the basic geology for the UK. More detailed sheets are available at scales of 1:250,000, 1:50,000 and 1:10,000. The 1:625,000 and 1:250,000 scales show both onshore and offshore geology (the 1:250,000 series covers the entire UK continental shelf), whilst other scales generally cover exposures on land only.

Sheets of all scales (though not for all areas) fall into two categories:

1. Superficial deposit maps (previously known as solid and drift maps) show both bedrock and the deposits on top of it.
2. Bedrock maps (previously known as solid maps) show the underlying rock, without superficial deposits.

The maps are superimposed over a topographic map base produced by Ordnance Survey (OS), and use symbols to represent fault lines, strike and dip or geological units, boreholes etc. Colors are used to represent different geological units. Explanatory booklets (memoirs) are produced for many sheets at the 1:50,000 scale.

Small scale thematic maps (1:1,000,000 to 1:100,000) are also produced covering geochemistry, gravity anomaly, magnetic anomaly, groundwater, etc.

Although BGS maps show the British national grid reference system and employ an OS base map, sheet boundaries are not based on the grid. The 1:50,000 sheets originate from earlier 'one inch to the mile' (1:63,360) coverage utilising the pre-grid Ordnance Survey One Inch Third Edition as the base map. Current sheets are a mixture of modern field mapping at 1:10,000 redrawn at the 1:50,000 scale and older 1:63,360 maps reproduced on a modern base map at 1:50,000. In both cases the original OS Third Edition sheet margins and numbers are retained. The 1:250,000 sheets are defined using lines of latitude and longitude, each extending 1° north-south and 2° east-west.

United States

In the United States, geological maps are usually superimposed over a topographic map (and at times over other base maps) with the addition of a color mask with letter symbols to represent the kind of geologic unit. The color mask denotes the exposure of the immediate bedrock, even if obscured by soil or other cover. Each area of color denotes a geologic unit or particular rock formation (as more information is gathered new geologic units may be defined). However, in areas where the bedrock is overlain by a significantly thick unconsolidated burden of till, terrace sediments, loess deposits, or other important feature, these are shown instead. Stratigraphic contour lines, fault lines, strike and dip symbols, are represented with various symbols as indicated by the map key. Whereas topographic maps are produced by the United States Geological Survey in conjunction with the states, geological maps are usually produced by the individual states. There are almost no geological map resources for some states, while a few states, such as Kentucky and Georgia, are extensively mapped geologically.