GEOG 370: Test 1

Inverse flattening

f^-1 = 1/f = a/(a-b)

Semi-major axis

half of the major axis

Azimuthal projections

-Planar projections, formed when a flat piece of paper is placed on top of the globe and a light source projects the surrounding areas onto the map -The North or South Pole is the center of the map, given that you are looking down or up at the Earth shows the true scale, but only from one specific point; used for airlines, epicenter of earthquakes, etc

Line layer

-connect the dots in a set order and then it becomes a vector line with each dot representing a vertex -the lines usually represent anything that is linear in nature such as rivers, roads, and pipelines

Point Layer

-points are used to represent features that are too small to be represented by polygons (ex: cities on a global scale). -the layer that just has points

The Antimeridian

180th meridian; line of longitude exactly opposite of the Prime Meridian; International Date Line

The Prime Meridian

The meridian, designated at 0° longitude, which passes through the Royal Observatory at Greenwich, England.

basemap

=raster data in a GIS as a background display for other feature layers sources: orthophotos from aeriel photo, satellite imagery and scanned maps

Meridians

A circle of constant longitude passing through a given place on the earth's surface and the terrestrial poles.

cylindrical projections

A map projection that is made by moving the surface features of the globe onto a cylinder.

Dymaxion Projection

A map that has minimum amount of distortion to the shape of the world's major land masses. (made up of triangles). An icosahedron shape, 20 sides

Conformal projection

A map that maintains the correct shape of features on the Earth but distorts their relative size to one another. used for angles, accurate local directions and used for most large scale maps

Geoid

A model of global mean sea level that is used to measure precise surface elevations. The actual shape of Earth, which is rough and oblate, or slightly squashed. Earth's diameter is longer around the equator than along the north-south meridians. We are on a three-dimensional planet which has ups-and-downs in addition to the side-to-side in a horizontal coordinate system on the surface. To handle the ups-and-downs, we have the vertical datum which gives a place to put the zero measurement. Mean sea level is often understood as the basis for our ups-and-downs. This is called the geoid.

Ellipsoid

A model of the rounded shape of earth. The most common reference ellipsoid in cartography and surveying is the World Geodetic System (WGS84). The Clarke Ellipsoid of 1866 and was recomputed for the North American Datum of 1927 (NAD27). When comparing NAD27 and NAD84, latitude and longitude coordinates can be displaced on the degree of tens of meters (with the same latitude and longitude coordinates).

raster

A raster data type is made up of pixel cells and each pixel has an associated value. Digital Photography is the best example of raster data type model. Raster grid format is data model for satellite data and other remote sensing data. For raster positions, it's simple to understand cell size. Advantages: 1. Better for storing Image data. 2. A powerful format for statistical and spatial analysis. 3. Easy and efficient overlaying. 4. Simple Data Structure. 5. Same Grid Cell for several attributes. Disadvantages: 1. Dataset can be large, storage space can be a problem. 2. Network analysis is difficult to perform. 3. Loss of information when using large cells. 4. Insufficient projection transformation. 5. Difficult in a representation of Topology connections.

Tissot's Indicatrix

A set of imaginary circles on the globe which when displayed on a map projection illustrate distortions in the map projection.

Sphere

A solid shape that is perfectly round like a ball. No faces, edges, or vertices.

Datum

A theoretically exact point, axis, or plane derived from the true geometric counterpart of a specific datum feature. The origin from which the location, or geometric characteristic of a part feature, is established. Horizontal datums give us the capability to measure distances and directions across the surface of the earth.

Mercator Projection

A true conformal cylindrical map projection, the Mercator projection is particularly useful for navigation because it maintains accurate direction. Mercator projections are famous for their distortion in area that makes landmasses at the poles appear oversized.

Winkel Tripel Projection

A type of pseudocylindrical projection map in which both the lines of latitude and longitude are curved and was adopted by the National Geographic Society in the late 1990s (replacing the Robinson projection).

Pseudo-Mercator (Web Mercator)

A variant of the Mercator Projection. A cylindrical projection onto a perfect sphere instead of ellipsoid.

georeferencing

Aligning geographic data to a known coordinate system so it can be viewed, queried, and analyzed with other geographic data.

Particularities of a UTM projection

Allows for global projections to stay in meters. Does not work well on smaller scales.

The International Date Line

An arc that for the most part follows 180° longitude, although it deviates in several places to avoid dividing land areas. When you cross the International Date Line heading east (toward America), the clock moves back 24 hours, or one entire day. When you go west (toward Asia), the calendar moves ahead one day.

The Equator

An imaginary circle around the middle of the earth, halfway between the North Pole and the South Pole. 0 degrees latitude

Parallels

Another name for lines of latitude

Example of a continuous (non-discrete) raster

Continuous rasters are grid cells with gradual changing data such as elevation, temperature, or an aerial photograph. A continuous raster surface can be derived from a fixed registration point. For example, digital elevation models use sea level as a registration point. Each cell represents a value above or below sea level. As another example, aspect cell values have fixed directions such as north, east, south or west. Phenomena can gradually vary along a continuous raster from a specific source. In a raster depicting an oil spill, it can show how the fluid moves from high concentration to low concentration. At the source of the oil spill, concentration is higher and diffuses outwards with diminishing values as a function of distance.

Discrete (categorical/thematic) raster

Discrete rasters have distinct themes or categories. Ex: one grid cell represents a land cover class or a soil type. In a discrete raster, you can distinguish each thematic class and each class can be discretely defined where it begins and ends. Discrete data usually consists of integers to represent classes (ex: value 1 represents urban areas and then value 2 represents forests.)

Longitude

Distance east or west of the prime meridian, measured in degrees

Latitude

Distance north or south of the equator

Semi-minor axis

Half of the minor axis

Polygon layer

Joining a set of vertices in a particular oder and then close it. Polygons are used to show boundaries and they all have am area.

Minimum and maximum values of latitude and longitude

Latitudes: -90° to 90° and Longitudes: 0° to 180°

How the values of N,S,E,W and the signs (-,+) change in longitude or latitude depending on your location on earth

Longitudes become negative west of the prime meridian and positive east of the prime meridian. Latitudes become negative south of the equator and positive north of the equator.

EPSG: 2264 common uses

North Carolina Projection

How scale may shape our decision to represent an object with a point, line or polygon.

On a global scale, points are used to represent cities, etc. On smaller scales, lines are usually used for roads and rivers, and polygons are used to represent buildings.

control points

Point locations where the coordinates are known--these are used in aligning the unreferenced image to the source

EPSG: 3857 common uses

Pseudo-Mercator Projection

Particularities of a SPCS projection

Solely created for the mapping of the United States and allows for great accuracy when looking at individual states.

Lambert's Cylindrical Equal Area Projection

The Lambert Conformal Conic is derived from a cone intersecting the ellipsoid along two standard parallels. When you "unroll" the cone on a flat surface, this becomes the mathematically developed surface. The most distortion occurs in the north-south directions. In general, distortion increases away from the standard parallels. For example, this map projection severely expands South America. (I am not sure if this is the same projection) the Lambert projection (SPCS); maps long east to west regions, but not good for whole world

General characteristics of UTM and State Plane projections

The UTM projection flattens the sphere 60 times by shifting the cylinder central meridian 6° for each zone and allows the map to always work in meters. It works horribly on a small scales. State Plane Projections are the some 120 geographic sections that break down the UTM or Lambert Conformal Projections of the US into sections. Very useful for when projecting individual states.

False easting

The linear value added to all x-coordinates of a map projection so that none of the values in the geographic region being mapped are negative.

False northing

The linear value added to all y-coordinates of a map projection so that none of the values in the geographic region being mapped are negative.

EPSG: 2163 common uses

US National Atlas Equal Area, used for true proportions, population density dot maps, land use and GDP (??)

Vector

Vector data represent the features as an individual point, and they are stored as pairs of (x, y) coordinates. If these points are joined, they create a lines feature, or if they joined into a closed ring, they create a polygon, but all vector data fundamentally consists of lists of coordinates that define vertices and paths. Vectors are frequently used in all kinds of applications. One common area is urban planning, where land parcels and buildings are often represented as polygons, roads as polylines or polygons (road edge), and small features like telephone poles are represented by points. Advantages: 1. Compact data structure - Need less space for storing data. 2. Accurate Graphic output. 3. Since most information, e.g. printed version maps, is in vector form no data conversion is required. 4. Exact geographic location of data is maintained. 5. Easily make a connection between topology and network, efficient for network analysis. Disadvantages: 1. The location of each vertex needs to be stored explicitly. 2. It has a complex Data Structure. 3. Difficult overlay operations. 4. high spatial variability is inefficiently represented. 5. Spatial analysis and filtering within polygons are impossible.

EPSG: 4326 common uses

WGS84 Projection

Decimal Degrees

When decimals are used to divide partial degrees instead of minutes and seconds.

conical projections

a map projection in which an area of the earth is projected onto a cone whose vertex is usually above one of the poles, then unrolled onto a flat surface.

Equal-area (equivalent) Projection

a map projection on which the areas of regions are represented in correct or constant proportions to earth reality

DMS

degrees, minutes, seconds

Great circle distance

the shortest distance between two points on a spherical surface