Cartography

the art, science, and technology of making various maps.

a closed quadric surface that is a three dimensional analogue of an ellipse

Spheroid

• approximates the shape of a sphere
• created by rotating an ellipse about either its major axis (called a prolate spheroid) or its minor axis (called an oblate spheroid)

Any straight line on map - line of constant direction

not the shortest distance between two points

provides the location of property-ownership lines with their bearings,length, ownership, and size

SLOB

any circle drawn on Earth’s surface whose center coincides with the center of Earth

Examples:

• Equator
• All meridians

• Good for navigation
• Gives you the shortest distance

The shortest distance between two points on Earth surface

circles whose centers do not coincide with the center of Earth

Examples:

All parallels except the Equator

• an imaginary line on the Earth's surface from the North Pole to the South Pole that connects all locations with a given longitude
• Each is half of a great circle on the Earth's surface
• the principal north-south line used for survey control in a large region

Map projections and coordinate systems are distinct concepts that serve two different purposes in georeferencing; Georeferencing Meaning finding locations

The function of map projections is to define how positions on the earth’s curved surface are transformed onto a flat surface

A coordinate system is then superimposed on the surface to provide the referencing framework by which positions are measured and computed

Taken together, the Clarke 1866 reference ellipsoid and the geoid origin of Meades Ranch comprimise the North American Datum of 1927 (NAD27)

However, since the advent of satellite geodesy, large errors have been encountered when comparing the results of today's highly accurate survey techniques with the NAD27 values

To remedy this, a new reference ellipsoid, the Geodetic Reference System (GRS), was recommended by the International Geodesy and subsequently adopted by the National Geodetic Survey, creating the North American Dantum of 1983 (NAD83)

When to use:

• NAD27: if you are in N. America, and want to match your NAD27 topo maps.
• NAD83: if you are in N. America, and are collecting raw data.
• WGS84: if you are going to compare with GPS data you have collected elsewhere in the world.

Datum

A datum is the mathematical model that fits the earth to an ellipsoid. It is a reference from real-world to this ellipse

• The earth’s surface is not perfectly round. Instead, it is ellipsoid, with mountains and valleys
• Datum are used to correct for these undulations (wavy surfaces).

• A datum is a geodetic reference system that specifies the size and shape of the earth
• Base point from which the latitude and longitude of all other points on the earth’s surface are referenced

Datums and the coordinate systems based on them were developed to describe geographic positions for surveying, mapping, and navigation

Over the years, datums evolved from spherical to ellipsoidal models using satellite measurements. The earth is not a sphere, but an ellipsoid flattened slightly at the poles and bulging somewhat at the equator

The ellipsoid is used as a surface of reference for the mathematical model of the earth. Since mathematical models of the size and shape of the earth are now more precise, it has become necessary to change to a more accurate model

Datum Shift

• Datum shifts are differences in the mathematical formulas between datum
• Datum shifts must be taken into account when re-projecting data, or comparing data of different datum, or else error will be introduced

a geographical device plotted on a map projection that illistrutates the kind and extent of distortion at infinitesimally small points

(best def) provides a visual means of showing how distortion varies at point locations across a projection (best def)

provides a quantitative analysis of distortion that describes the amount and type of distortion that occurs at points across a map

State Plane Cordinate System

Uses the Lambert Conformal Conic Projection for states like Tennessee and Oklahoma

Uses Transverse Mercator Projection for states like Illinois

set of 124 geographic zones or coordinate systems designed for specific regions of the United States

Each state contains one or more state plane zones, the boundaries of which usually follow county lines

• 60 UTM Zones
• each zone covers 6° longitude
• False origin, false easting, false northing, Central meridian (500000 m, 0 m) (fancy way of saying x.y)
• State of Illinois: zone 15 and zone 16
• Use zone 15 as an example to explain how UTM is defined: false origin (0 m, 0m) on the Equator, central meridian (93º w)

Map are especially effective devices for recording and communicating information about the environment

Maps clearly preserve the locational attributes of that information (i.e., show the relationships between one feature and another)

Maps can also indicate distances and directions between locations, or the areas occupied by different types of land uses or features

Maps are useful for determining the patterns formed by many types of distributions on the earth surface (e.g., roads, villages, cities, streams, lakes, …)

neatly drawn, bird's eyed view of the earth’s surface

graphic representations of the environment, both cultural and physical

Equivalent

preserves area

When a map portrays areas over the entire map so that all mapped areas have the same proportional relationship to the areas on the Earth that they represent, the map is an equal-area, or equivalent, map.

Conformal

preserves shape

When the scale of a map at any point on the map is the same in any direction, the projection is conformal. Meridians (lines of longitude) and parallels (lines of latitude) intersect at right angles.

a systematic transformation of the Earth's graticule and landmass from the curved two dimensional surface to a flat two dimensional planimetric surface

The line of tangency between a projection surface (cylinder or cone) and the surface of the reference is called the standard line of the projection. If it is along a parallel, as is often the case, it is called the Standard Parallel

There is no distortion along the standard line(s) because there is a one-to-one relationship between the projection surface and the globe. Away from the standard line, however, distortion occur

Central meridian is the longitude that is designated as the center of the map projection

a surface that can be flattened to form a plane without compressing or tearing any part of it

three commonly used developable surfaces for map projections are:

• cylinder
• cone
• plane

latitude

imaginary line that crosses the earth's surface in an east to sest fashion

measured in degrees, minutes, seconds north or south of the equator

SHAPE

• When the scale of a map at any point on the map is the same in any direction, the projection is conformal.
• Meridians (lines of longitude) and parallels (lines of latitude) intersect at right angles

AREA

When a map portrays areas over the entire map so that all mapped areas have the same proportional relationship to the areas on the Earth that they represent, the map is an equal-area, or equivalent, map

DISTANCE

A map is equidistant when it portrays distances from the center of the projection to any other place on the map

DIRECTION

A map preserves direction when azimuths (angles from a point on a line to another point) are portrayed correctly in all directions.