Geographic concepts and spatial data Adina Racoviteanu Lecture

Geographic concepts and spatial data Adina Racoviteanu Lecture # 2, GEOG 4103 spring 2006

Outline • • • Spatial Cognition Types of objects Scale Spatial measurement levels Spatial patterns

Human perception of the world • world consists of objects, events, processes, and a background environment • cognition = acquisition, storage and retrieval, manipulation, and use by living creatures • Similar process in GIS

Spatial cognition • cognition of spatial properties of the world: – location – size – distance – direction – shape, pattern, movement, and inter-object relations.

Cognitive Maps • “ Mental maps” • internal representations of the world and its spatial properties stored in memory • can sometimes be distorted (eg. size, shape)

Geospatial data • Two main components: – Spatial component: Where is it? – Non-spatial (thematic) component: What is it?

Spatial data Location = spatial mode of information 1) Absolute location: e. g. geographic position: (x, y) latitude, longitude 2) Relative location

Attribute data • Non-spatial • Attributes =characteristics of objects A table showing the attributes of objects is called an attribute table Name Area Object_1 100 Object_2 200 Elevation 5077 5999 Columns = attributes Rows = objects

What types of geographic objects? • Point data Zero-dimensional (x, y) • Line data One-dimensional (x, y, length) • Area data Two-dimensional (x, y, length, width) • Continuous data Three-dimensional (x, y, length, width, height) volumetric

Scale • Large-scale vs. small-scale • Objects depicted are large • Covers small areas • More detailed • E. g trekking maps, campus map • Objects depicted are small • Covers large areas • Less detailed • Eg. World map

Scale

Generalization

Data measurement levels • Nominal: “named” data – e. g. phone numbers, codes etc… • Ordinal: ranking – measurements differ by order, e. g, 1 st, 2 nd, 3 rd. . – Data can be compared, but only qualitatively • Interval: – Used to quantify differences between measurements, eg. Temperature, distance etc… – Zero point (point of begninning) is arbitrary • Ratio: – Used to quantify ratios, and to compare one measurement to another – Zero point is absolute

Example: • Distance 30 miles origin A B

Geographic Inquiry • • • location and extent; distribution and pattern or shape; spatial association; spatial interaction; Spatial/temporal change

Spatial patterns Regular Random e. g. tree distribution Clustered

Why do data display this spatial pattern (distribution)? • Associations – E. g. apple trees grow in moister environments • Spatial correlations – E. g. there is a relationship between density of trees and terrain slope

Data collection process • Type of data collected depends on the scale we want to look at; • What area needs to be covered? • What is the amount of detail needed? – Small scale: remote sensing imagery – Larger scale: aerial photography – Large scale: field sampling, e. g. GPS

Cartographic maps • Representations of the world • communicate geographical information • Distortions: – projections – scales – perspectives etc. .

Maps as Models Maps are models of reality. They emphasize some aspects of reality in a cartographic representation while ignoring or greatly simplifying other aspects of reality.

Scale the amount of reduction in the representation of a real world geographic phenomenon on a map. or, the ratio of map distance to earth distance 1: 24, 000 verbal scale 1 inch = 2000 ft representative fraction bar scale 1 2000 ft

More on maps next time…