GIS’s Roots in Cartography Getting Started With GIS Chapter 2

Organizing Data and Information l Information can be organized as lists, numbers, tables, text, pictures, maps, or indexes. l Clusters of information called data can be stored together as a database. l A database is stored in a computer as files.

The GIS Database l In a database, we store attributes as column headers and records as rows. l The contents of an attribute for one record is a value. l A value can be numerical or text.

Flat File Database RecordValue Attribute RecordValue RecordValue

The GIS Database (ctd) l Data in a GIS must contain a geographic reference to a map, such as latitude and longitude. l The GIS cross-references the attribute data with the map data, allowing searches based on either or both. l The cross-reference is a link.

Latitude What is Latitude? l Lines of Latitude run horizontally l Latitude is measured in degrees. l The Equator is 0 degrees Latitude. l Lines of Latitude locate places North or South of the Equator. l The North Pole is 90 degrees N Latitude, and the South Pole is 90 degrees S Latitude.

Longitude l Lines of Longitude run vertically. l They are also called Meridians. l The Prime Meridian is found in Greenwich, England. l The Prime Meridian is 0 degrees Longitude. l Lines of Longitude locate places East or West of the Prime Meridian. l There are 180 degrees of east Longitude, and 180 degrees of west Longitude.

Time Zones l Time zones are broad strips that measure 15 degrees wide. l Time zones differ from their neighboring time zones by 1 hour. l The continental U.S. has 4 time zones, Eastern, Central, Mountain, and Pacific. l In the Spring we shift the clocks 1 hour ahead. This is called Daylight Saving Time. l In the Fall we shift the clocks 1 hour back.

Time Zones (cont…) Local Time and Universal Time Local Time- is what we use everyday, and regulates our lives. Examples of Local Time are: meal time, sleep time, work time, and school time Universal Time- is what we use when we need a time that is agreed upon marking time world-wide. An example when Universal Time was used when a supernova in 1987 was first seen. Astronomers, and Astronauts use Universal Time.supernova

Time Zones (cont….) l Greenwich Mean Time- is the time that is registered at Greenwich, England. **Greenwich Mean Time is another name for Universal Time. The International Dateline was established following the 180th meridian, where ever we cross it the date advances 1 day ( if you are going west), or goes back 1 day (if you are going east).

Summary 1.What do lines of Latitude and Longitude combine to make? A grid. 2.Compare and Contrast Latitude and Longitude. Latitude- horizontal, north- south, parallels Longitude- vertical, east-west, meridians 3.What is 0 degrees Latitude? Equator 4.What is 0 degrees Longitude? Prime Meridian 5.How many time zones do we have in the U.S.A.? 4- Eastern, Central, Mountain, Pacific 6. Explain the difference between Local Time, and Universal Time. Local time- used everyday Universal Time- is used for a planetary event, or for astronomy

Latitude lines run east/west but they measure north or south of the equator (0°) splitting the earth into the Northern Hemisphere and Southern Hemisphere.

Latitude Lines of latitude are numbered from 0° at the equator to 90° N at the North Pole. Lines of latitude are numbered from 0° at the equator to 90° S at the South Pole.

Latitude The North Pole is at 90° N The equator is at 0° latitude. It is neither north nor south. It is at the center between north and south. The South Pole is at 90° S 45° N is the 45° line of latitude north of the equator. 45° S is the 45° line of latitude south of the equator.

Longitude Lines of longitude are numbered east from the Prime Meridian and west from the Prime Meridian. PRIME MERIDIAN West Longitude East Longitude 0° N EW S North Pole

Longitude Lines of longitude begin at the Prime Meridian. 60° W is the 60° line of longitude west of the Prime Meridian. The Prime Meridian is located at 0°. It is neither east or west 60° E is the 60° line of longitude east of the Prime Meridian. WE

Prime Meridian The Prime Meridian (0°) splits the earth into the Western Hemisphere and Eastern Hemisphere. Western Hemisphere Places located east of the Prime Meridian have an east longitude (E) address. Places located west of the Prime Meridian have a west longitude (W) address. Eastern Hemisphere Prime Meridian

Any location north of the equator is a NORTH LATITUDE

Any location south of the equator is a SOUTH LATITUDE

Any location west of the prime meridian is a WEST LONGITUDE

Any location east of the prime meridian is an EAST LONGITUDE

By combining latitude and longitude, any location can be pinpointed

Each box on this map is 15°. With that in mind how can we identify specific locations (red dots)? Remember, write latitude first! What are the coordinates of location......A 60°N, 30°W What are the coordinates of location......B 15°S, 105°W What are the coordinates of location......C 75°S, 75°E But what about location D ? It’s in the middle of a box. What do we do now?

Here are some things to remember: > Latitude is written first and must always include N (north) or S (south) of the equator. > Longitude is written next and must always include E (east) or W (west) of the prime meridian.

See If You Can Tell In Which Hemispheres These Lon/Lats Are Located l 1. 41°N, 21°E l 2. 37°N, 76°W l 3. 72°S, 141°W l 4. 7°S, 23°W l 5. 15°N, 29°E l 6. 34°S, 151°E AB C D

l 1. B l 2. A l 3. C l 4. C l 5. B l 6. D

Now you’re ready to find some locations on a map!

Cartography and GIS l Understanding the way maps are encoded to be used in GIS requires knowledge of cartography. l Cartography is the science that deals with the construction, use, and principles behind maps.

Map Scale l Map scale is based on the representative fraction, the ratio of a distance on the map to the same distance on the ground. l Most maps in GIS fall between 1:1 million and 1:1000. l A GIS is scaleless because maps can be enlarged and reduced and plotted at many scales other than that of the original data. l To compare or edge-match maps in a GIS, both maps MUST be at the same scale and have the same extent. l The metric system is far easier to use for GIS work.

Map Projections l A transformation of the spherical or ellipsoidal earth onto a flat map is called a map projection. l The map projection can be onto a flat surface or a surface that can be made flat by cutting, such as a cylinder or a cone (Figure on Next Slide) l If the globe, after scaling, cuts the surface, the projection is called secant (Secant is a term in mathematics derived from the Latin secare ("to cut")). Lines where the cuts take place or where the surface touches the globe have no projection distortion.

Map projections (ctd)

Map Projections (ctd) l Projections can be based on axes parallel to the earth's rotation axis (equatorial), at 90 degrees to it (transverse), or at any other angle (oblique). l A projection that preserves the shape of features across the map is called conformal (a conformal map is a function that preserves angles locally). l A projection that preserves the area of a feature across the map is called equal area or equivalent. l No flat map can be both equivalent and conformal. Most fall between the two as compromises. l To compare or edge-match maps in a GIS, both maps MUST be in the same projection.

“no flat map can be both equivalent and conformal.”

Coordinate Systems for the US l Some standard coordinate systems used in the United States are –geographic coordinates –universal transverse Mercator system –military grid –state plane l To compare or edge-match maps in a GIS, both maps MUST be in the same coordinate system.

Building complex features l Simple geographic features can be used to build more complex ones. l Areas are made up of lines which are made up of points represented by their coordinates. l Areas = {Lines} = {Points}

Areas are lines are points are coordinates

Properties of Features l size l distribution l pattern l Contiguity (series of things) l neighborhood l shape l scale l orientation.

Basic properties of geographic features

GIS Analysis l Much of GIS analysis and description consists of investigating the properties of geographic features and determining the relationships between them.