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What are geologic maps?
Geologic maps show the distribution of rocks at the Earth's surface. Usually, the rocks are divided into mappable units that can be easily recognized and traced across an area. The divisions (contacts between units) are based on color, texture, or rock composition. Geologic maps only show what is exposed at the surface of the Earth.
What are cross
sections? - Geologic cross sections are drawings of a vertical slice through the Earth.
Definitions:
Cartography
The science of mapping
Quadrangle
Four-sided figure
Neat Lines
The boundaries of quadrangle maps. Makes the maps look neat
Prime Meridian
Zero degrees longitude. Also known as the Greenwich Meridian
7.5 Minute Quadrangle
Cover land measuring 7.5 minutes of arc from north-south and east-west. At a scale of 1:24000, covers from 49-70 square miles.
Latitude
North-South, read before longitude
Longitude
East-West, read after the latitude
Quadrangle Name
Appears in the upper right corner, may be named after a prominent city, feature, or town. Most of that feature must lie within the quadrangle for the quad to be named after it, the state name is also here.
Type
Appears in the upper right corner. Two types of type: topographic and planimetric
Topographic Type
Shows the shape and elevation of the land
Planimetric Type
does not show the shape and elevation of the land but the horizontal orientation and natural and manmade (cultural) features
Title Block
does not show the shape and elevation of the land but the horizontal orientation and natural and manmade (cultural) features.
Plant Imprint Note
located in the lower right margin. includes the name of the government department responsible for making the map and the name and location of the printing plant. the location above is used for USGS maps.
Legend
located in the lower right margin. shows the classes of roads and route markers on the map scale
Scale
(on 7.5 maps) expressed in two ways: a fixed ratio or direct proportional/ diagrammatic bar scales. both are found in the lower margin.
Contour Lines
fine, curving brown lines, the same elevation. Depict the shape and elevation of the land.
Contour Interval
the vertical difference between adjacent contour lines. this value is printed beneath the feet/ kilometer bars in the lower margin.
National Map Accuracy Standards
in the lower center margin. makes sure that a map complies with government standards. if this is not present then the map does not meet the standards.
Declination
the angular difference between true north and magnetic north
Graticule Tick Marks
help in mentally dividing the map into nine equal pieces called sectors.
Sectors
nine equal parts of the ma, they are numbered from left to right in three rows. Do NOT confuse this term with section.
Class 1 Buildings
structures primarily meant for housing human activities, these are shown by a solid or crosshatch print.
Class 2 Buildings
NOT meant for housing human activities, depicted by an open outline or a single hatch, with the hatch running northeast-southwest (diagonal) direction.
Landmark Buildings
serve the community or have specific importance, so they are shown on maps.
Major Highways
shown in solid red
Other Roads
parallel black lines
Secondary Highways
red between white lines
Index Contour Lines
thick brown lines with elevations marked at frequent intervals
Immediate Contour Lines
thin, light brown lines, in between the index contours.
Depression Contours
show depressions or pits in the land shown by closed contours with right angle tick marks pointing inward.
Supplementary Contours
shown on maps of flatter areas to show features less than the basic interval. shown as dashed or dotted lines.
Cut and Fill Contours
shown conditions on large areas around roads that define the local terrain with less than a contour interval, shown by hachures along the contour.
Ridge
shown by contours that form a successive 'v' or 'u' pattern.
Perennial Pond or Stream
these bodies of water are always present except during major draughts, they are shown by solid blue lines or solid blue lines with a light blue fill.
Intermittent Pond or Stream
these contain water only during a certain part of the year. The streams are shown by blue dashes separated by three blue dots. The lakes are shown by a solid blue outline filled with light blue diagonal hatching. The ponds are shown by a dashed blue outline filled with light blue diagonal hatching.
Rule of the V's
the phrase that refers to the shape that a contour line has when it passes through a stream. the point of the 'v' points upstream.
Control Data
these marks or symbols identify latitude and longitude, elevation or all.
Horizontal Control Station Marks
marks for which latitude and longitude have been determined. on quad maps, they are shown as black outlined triangles with a dot in the center or the same as above plus the letters 'BM' (meaning benchmark) and the elevation. On the actual site, it is a metal tablet or other permanent type marks.
Gradient and Slope
Gradient elevation change per 1000 ft, slope elevation change per 100 ft
Vertical Control Station Marks
marks the place where elevation has been determined. On USGS topo maps this is shown by a black 'x' and labeled 'BM' for benchmark. The elevation is written in black numbers. on the actual ground, they are metal tablets or other permanent marks.
Spot Elevation
less accurate than benchmarks but more accurate than contour lines. Unless the locations are obvious, like a road intersection, these will be marked by small blacks 'x's with the elevation printed in black slanted type. (this is for topo maps) Number values of spot elevations which have not been accurately surveyed are printed in brown.
Water Surface Elevation
these are for large lakes and reservoirs. they are based upon the normal level of water. the elevations of these bodies of water are printed in black slanted type within the body of water on the map. max. water depths are shown in blue slanted type.
Finding Latitude and Longitude
2-1/2º = 150 minutes. Find proportions.
Sedimentary Facies
Rocks that formed at the same time but in different depositional environments
Lithification
The binding together of sedimentary particles to form a coherent sedimentary rock
Epoch
a period of time in history or a person's life, typically one marked by notable events or particular characteristics.
Stratigraphy
geology that deals with the origin, composition, distribution, and succession of strata
True Dip
tan(true dip) = tan(apparent dip)sin(angle between strike and apparent dip direction)
