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Introduction to GIS Introduction to GIS

Paolo Zatelli | Università di Trento | 1/22

Introduction to GIS

Paolo ZatelliDipartimento di Ingegneria Civile, Ambientale e Meccanica

Università di Trento



System: set of resources and procedures

Information: it is based on an information system

Geographic: all the information has a spatial reference

Geographic Information System



Resourceshumaninfrastructuresdata

Procedures

acquisitionarchivingprocessingpresentationtransmission

data

System



GISs are based on information systems and procedures:• generic• proprietary

Current systems use generic/standard hardware and software wherever possible (es. DBMS).

The choice of the right system depends on the purpouse.

Information System



All the features are spatially referenced

the basis for GISs is the numerical cartography

The system manages• geometry• topologyand their relationships with attributes (database).

Geographic Information System



Data are the most precious part of a GIS (except for HR!):• high production cost;• need of updates;• impossibility of recover (if data are lost and the objects they describe have changed).

They consists in• geometry;● attributes;● metadata.

Data



Numerical surveydesigned for the use of output data in a GIS

Pre-existing datafor non-GIS use

Traditional survey techniques• topographic• photogrammetric

Modern survey techniques• remote sensing• GPS• laser scanning• SAR

Existing documents• cartography• “data base”

Dipartimento di Ingegneria Civile e Ambientale Università di Trento

Data production



Acquisition

Primarymeasurements and data processing

Secondarydigitazingscanningattribures encoding

Data

geometryvectorrasterdigital image

attributes database

Data acquisition

Numerical surveydesigned for the use of output data in a GIS

Pre-existing datafor non-GIS use



Modeling External

Conceptual

Logical

Internal

external to GIS

modeling of the problem

data, tables, maps structure

file structure, ecc.

Data modeling



Map• geometric features (points, lines, areas)• attributes• legend (links attribures to features)

Non-spatial attributes are represented with symbols, colors, etc.

Planimetry is separate from altimetry (height=attribute of points or lines, contour levels).

Traditional cartography



Local and global knowledge of a region

Detection of the mutual relationships between features

Relationships between features are detected by the reader of the map, this process must be coded and made automatic for numerical cartography, to apply algorithms using these relationships.

Use of the map



A set of• coordinates associated to features (points, lines, areas)• relationships between features• features' attributes

It can be seen as mirror situation with respect to a traditional map tradizional map: drawing coordinates

numerical cartography: coordinates drawing

Numerical cartography contains more information and allows a broader range of use with respect to the traditional map (which can be created from numerical cartography, anyway).

Numerical cartography



The concept of scale seems to be useless in numerical cartography because it possibile to display/print a map with an arbitrary zoom factor, since coordinates are absolute.

Actually, in cartography,scale depends on the coordinates' accuracy.

Nominal scale: scale corresponding to a traditional map with the same metric requisites (accuracy accuracy of the plotter, usually 0.1-0.2 mm).

Scale



Qualitative content of a map depends on the scale

Large scale → drawingSmall scale → symbol

Most of the current GISs do not automatically select the way a feature is displayed as a function of the scale (generalization).

Generalization



Relationshipsdirectionaltopologicalneighborhood

Directional relationships: depend on map orientation.

facingon the other sideabovebelow

northsoutheastwest

and combinations

Spatial relationships between features



Equivalence

Separation

Proximity

Containment

Partial equivalence

Topological relationships



they evaluate in quantitative and qualitative ways the distance between features:

Qualitative•near•far•close to

Quantitative

d=1234m

Neighborhood relationships



In numerical cartography features layers are usually separate

hydrography

settlements

primary roads

Layers



In the environmental field, main uses are:• to create thematic maps, displaying the spatial distribution of phenomena (e.g. avalanche locations, population distribution, etc.)• to setup models of phenomena occuring on a region (e.g. a model of the risk of avalanche, a model of distribution of fauna).

Use of GISs

GISs are used whenever information has a spatial component (i.e. information is directly o indirectly connected to coordinates).



Thematic map – population by country



Avalanche risk model

Sup.criticaPascolo

Bosco rado

Bosco denso

Improduttivo

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