Support the spread of “good practice” in generating, managing, analysing and communicating spatial information Introduction to GIS for the Purpose of Practising PGIS Visualising Spatial Information and Relationships By: Jon Corbett and Kasondra White Unit: M12U02

Visualising spatial information and relationships Communicating spatial phenomena and ideas Enhancing dialogue Displaying data Confidence in data Map types Symbols

Displaying data Different types of data are used by GIS File format represents data type Distinguished by file extension Some examples include: –.shp –.dbf –.prj

Raster data Pixels are used to represent images Image divided into a grid Each cell contains information Straightforward and easily understandable visualisation Quality lost when image is magnified Require more storage space

Raster data

Vector data Based on points, lines and polygons Mathematical representations of images Accuracy of geographic features maintained Less capable of representing continuous images

Vector data

Revisiting the layer Geospatial data are organised into different themes Arranging layers hierarchically Examining interrelationships between layers Overlay – using one or more thematic layers to create a new map or series of maps

Confidence in data Understanding data origins Examining metadata (i.e. data about other data) It is important to: –be aware of the range of data covered –know when the data were collected –understand the goals of the individual or agency responsible for creating the data

Database management Attribute tables Adding information to pre-existing layers Viewing data on the map Viewing data within the Attribute Table

Types of data Attributes –characteristics associated with features on the map –information is displayed in Attribute Tables Examples of attribute data include: –the square footage of a building –the names of land-use types –average incomes of inhabitants –names of community locations or routes

Types of data Spatial data –define the absolute position of an object –use X and Y coordinates –reflect size and shape in real world terms –features must be aligned with known geographic locations (“georeferencing”)

Map types Maps are: –stylised representations of the world –abstractions –a representation of the Earth’s surface Features included are at the map maker’s discretion Constant rate of change means maps are often out of date

Aerial photos Digital images of the Earth from the air Raster images Can be a useful base layer Fairly accurate representations Subject to pixelisation when magnified

Aerial photos

Line maps Generally vector images Illustrate features using lines and symbols Street maps Used for drawing out specific points of interest

Line maps

Topographic maps Concerned with depicting the topography of the Earth’s surface Characteristics of features such as: –lakes –mountains –human-made items Depict contours and elevation of features

Topographic maps

3-D Aligns more closely with how human beings see information Adds an element of depth Uses a Z coordinate

3-D

Symbols GIS employ a range of symbols to represent features Used to reference specific points on a map Align with X and Y coordinates Convey meaning independent of language