Lecture 1

Principles of GIS( UNSW Metternicht )

outline:data input---data management---data manipulation+data analysis---spatial modelling

Definition

1. GIS is a tool to digitally abstract the real world, information is connected to its physical location and organized into layers.

2. a GIS consists at least information database( with attribute ), map information, computer-based link between them.

GIS storement

1. people manage database information by layer or theme

2. a value can be a number or a text

type of data( vector矢量 raster栅格)

1. spatial data (空间数据): has location information, giving the information about where is it, can be mapped, spatial data models begin with conceptualization, how you will represent the real world phenomena or entities( road, river, etc.), which is the objects in a spatial database plus the relationships among them.

2. attribute data: giving the information about what is it.

3. topology(拓扑): what related to this feature

attribute data

1. nominal attributes: provide descriptive information about an object (for example, colors、city names or vegetation type), which can also be images, audios or other kinds of descriptive information.

2. ordinal attributes: imply rank order or scale by their values ( for example, small、medium、large, ranking from 1 to 10 ).

3. interval or ratio attributes: are used for numeric items where both order and difference in magnitudes( 量级 ) are reflected in number( real number in a linear scale, for example: height、weight, etc.)

data model concept

1. vector data model: discrete objects (point,lines)

2. raster data model: continuous phenomena (use grid cells)

vector data model

1. point: to represent the location

2. line: to represent linear features

3. polygon: represents entities which covers an area

raster data model (cells)

rasters are digital aerial photographs, imagery from satellites, digital pictures, or even scanned maps

TIN data model---tesselations (Triangulated Irregular Network)

1. TIN is a data model commonly used to represent terrain (地势) heights, which will be describes as x,y, and z locations.

2. TIN used for digital elevation models (DEM) or digital terrain models (DTM).

vector data

1. can be multipart

2. polygons can have holes

3. holes can contain islands

4. can overlap

vector model

the direction of a line is determined by the order of its vertices (制高点)

polygon exteriors  (外观) are stored in an anticlockwise(逆时针) order

顺时针方向为内孔方向（Internal holes）

total area of the polygon areas is the sum of the part areas

raster data

a cell’s coordinate is inferred from its file order, the cell size and corner coordinates (坐标)

nodata means the value is not known or is not relevant