–combines elements of computer science –database design –software design geography –map projections –geographic reasoning mathematics –mathematical topology –logical analysis –has tended to be Canadian and European Geomatics

Alternative terminology geographic information systems –properly emphasizes geographic component –minimizes computer science spatial information systems –perhaps focuses too much on “information systems” land information systems –deals with the cadaster

Why consider new term(s) computer science issues are becoming much more critical role of database systems is becoming more critical –SQL 3 Open GIS efforts reducing role of proprietary systems focuses on analysis

Consideration of fundamental issues how is “reality” organized most of us assume that this is obvious BUT it isn’t it has major implications of what we can do with data and how consider entity versus field not just a minor issue

Entity vs field (part 1) (some simple discussions more later) entity partitioning reality into divisible units –this is a thing and that’s not –examples soil mapping unit forest stand city block neighborhood but how do you divide

Entity vs field (part 2) phenomena exists everywhere and is potentially different everywhere –examples elevation soil pH number PPM of chemical in air how can you map continuous data that is everywhere different

Entity vs field (part 3) fields can be converted to entities –all locations where soil pH > 7 and all where < 7 entities can be represented by fields –soil unit represented by pH of soil unit basically different spatial data used to represent –raster vs vector different operations etc etc etc

Entity phenomena that cannot be subdivided into like units but can have components –e.g. entity house cannot be subdivided into houses can be divided into rooms indivisibility based on the properties used in the definition –entities can be very different as long as the definitional criteria are same e.g. lake –can be big or small have pollution or not e.g. polluted late or big lake –in this case the size or presence/absence of pollutants does affect entity

Entity versus object entity is conceptual organization of phenomena object is digital representation of a specific case of the entity more on this later

Types of data associated with (spatial) entities identifier (name, ID number, code number) position - may be coordinates (x,y) but might be an address, zip code spatial properties - distance to next entity, area, depth –don’t confuse a set of positional coordiantes with spatial properties –spatial properties may “use” or be “based on” coordinates but are not the same thing attribute - defined characteristic - number of residents, pH

Attributes defined characteristic of an entity –conditions/characteristics of entities which are not part of the definition pavement type is an attribute of the entity “highway” pavement type is part of the definition of the entity “asphalt highways” may be behavioral, functional or compositional

Attributes and entities entity - primitive unit (stream, factory) instance - specific occurrence (Buffalo River, Campbell’s Soup Plant) object - digital representation in computer of one or more instances spatial type - way entity represented in system - point, line, area attribute - characteristic of entity (stream flow, number of employees) attribute value - particular measure of attribute for instance (3300 cfs, 450 employees)

Spatial dimensions traditional types of spatial entities –points - x, y coordinate pair “dimensionless” –lines - sets of connected x,y coordinate pairs one dimension - length –areas - sets of at least 3 x,y coordinate pairs that start and end at the same pair two dimensions - length and width –volumes - sets of at least 3 x,y,z coordinate tuples three dimensions - length, width and depth

In fact (almost) everything has three dimensions –only things that doing are conceptual things starting point for the survey of the NW territory –it is usually only the map representation of things that can take on these characteristics –map scale is related to spatial dimensions oils well at 1:100,000 versus 1:200 scale street at 1:24000 scale versus 1:1200 scale

Spatial entities representation in database Initial introduction general concept of database representation one or more tables –each table representing one entity class (e.g. streams) each table has a set of rows and columns –each row represents one instance of the entity (Buffalo) –each column in row stores attributes about specific instance (width, CFS, or coordinates of points) –columns may be positional attributes or others

Geometric elements generally geometric elements are what are stored and manipulated in a computer representation of a spatial entity some terms –line segment: straight line connecting two points –string/polyline: set of line segments –chain: set of line segments connected at nodes (also arc) x x x x

Geometric elements (part 2) node: point that terminates a line or where line cross a single straight line segment that connects two nodes is a link –link can also be called edge –and an arc L&T prefer to have arc defined as a set of points (not the lines) that defining a string –may be spline curve or polynomial function

Geometric elements (part 3) ring –class of features that begin and end at same point closed polyline or ring of strings ring of arcs ring of links ring of chains

Combinations of entity types different entity types can be combined in many different ways in –queries –complex entities (compound entities) –transformations (more later) –duals (more later

Combinations of entity types