Applied Cartography and Introduction to GIS

GEOG 2017 ELLecture-1

Chapters 1 and 2

What is GIS?

A Geographic Information System (GIS) is a computer system for capturing, storing, querying, analyzing and displaying geospatial data.

GIS Components

• Computer hardware• Software• People• Infrastructure

GIS Operations

• Spatial data input• Attribute data management• Data display• Data exploration• Data analysis• GIS modeling

What is Geospatial Data?

Geospatial data are the data describing both the locations and characteristics of spatial features, such as roads, land parcels, and vegetation stands on the Earth’s surface.

Geographically Referenced Data

The street network is based on a plane coordinate system. The box on the right lists the x- and y-coordinates of the end points and other attributes of a street segment.

Coordinate System

• Geospatial data are geographically referenced.

• Two spatial reference systems used in GIS are the geographic coordinate system and the projected coordinate system.

• Projection connects the two spatial reference systems.

Vector and Raster Data Models

The vector data model uses x-, y-coordinates to represent point features (a), and the raster data model uses cells in a grid to represent point features (b).

Vector-Based Overlay

A vector-based overlay operation combines spatial data and attribute data from different layers to create the output.

Raster-Based Overlay

• A raster data operation with multiple rasters can take advantage of the fixed cell locations.

Layers and Coordinate System

Two map layers are not going to merge spatially unless they are based on the same coordinate system.

Layers and Coordinate System

The top map shows the interstate highways in Idaho and Montana based on different coordinate systems. The bottom map shows the connected interstate networks based on the same coordinate system.

Geographic Coordinate System• The geographic coordinate system is the location reference

system for spatial features on the Earth’s surface.

• The geographic coordinate system is defined by longitude and latitude.

Longitude and Latitude

A longitude reading is represented by a on the left, and a latitude reading is represented by b on the right. Both longitude and latitude readings are angular measures.

Approximation of Earth’s Shape

• The simplest model is a sphere, which is typically used in discussing map projections.

• But the Earth is not a perfect sphere: the Earth is wider along the equator than between the poles. Therefore a better approximation to the shape of the Earth is a spheroid, also called ellipsoid, an ellipse rotated about its minor axis.

Earth FlatteningThe flattening is based on the difference between the semi-major axis a and the semi-minor axis b.

Datum

• A datum is a mathematical model of the Earth, which serves as the reference or base for calculating the geographic coordinates of a location.

• A shift of the datum will result in the shift of positions of points.

Map Projection

• A map projection is a systematic arrangement of parallels and meridians on a plane surface.

• Cartographers group map projections by the preserved property into conformal, equal area or equivalent, equidistant, and azimuthal or true direction.

• Cartographers also use a geometric object (a cylinder, cone, or plane) and a globe (i.e., a sphere) to illustrate how to construct a map projection.

Different Map Projections

Aspect and Projection

Map Projections

NENW

SESW

Common Map Projections

• Transverse Mercator

• Lambert conformal conic

• Albers equal-area conic

• Equidistant conic

• Web Mercator

Projected Coordinate Systems

• The Universal Transverse Mercator (UTM) grid system

• The Universal Polar Stereographic (UPS) grid system

• The State Plane Coordinate (SPC) System

• The Public Land Survey System (PLSS)

UTM ZonesUTM zones range from zone 10N to 19N in the conterminous United States.

UTM Zone

A UTM zone represents a secant case transverse Mercator projection. CM is the central meridian, and AB and DE are the standard meridians. The standard meridians are placed 180 kilometers west and east of the central meridian. Each UTM zone covers 6° of longitude and extends from 84°N to 80°S.