Regions Chapter 15
Introduction • Regions are higher level objects built on tip of simple arcs and polygons. • Regions are organized into region layers or subclasses. • Region consists of polygons that may or may not be connected spatially. • Regions of different subclasses may overlap,
Introduction • Corresponds to concept of geographic regions • Ethnic, linguistic, ecologic regions. • May overlap and include spatially joint or disjoint areas. • Vector data!
Geographic Regions • Uniform regions are a geographic area with similar characteristics. • Example, uniform landform regions or uniform vegetation, etc. • Uniform regions defined by multiple themes • Omernik’s ecoregions: land use, potential natural vegetation, land surface form, soils and other supporting data.
Hierarchical Regions • Hierarchical regions represent different spatial scales of a hierarchy. • Census data compiled by state, county, census tract, block group, and block. • USGS hydrologic units organized in nested hierarchy: regions, sub-regions, accounting units, and cataloging units.
Hierarchical Regions • Ecological units are more complex examples of hierarchical regions: ecoregion, subregion, landscape, and land unit. • Climate and landform define ecoregion and subregion boundaries. • Relief, geologic parent materials, and potential natural communities + climate and landform define landscape boundaries. • Topography, soil characteristics, and plant associations + landscape define land units. • Canadian ecological land classification
Applications of the Regions Data Model • Building geographic regions • Either polygons or regions • Use maps of ecological units to create region subclasses for integrated coverage. • Advantages • Nested, overlapped and disjoint • Simple management • More efficient query and analysis
Applications of the Regions Data Model Disadvantages • Requires large storage and extra processing time • More difficult to revise or update (must rebuild entire integrated coverage • More difficult to manipulate (errors in clip, erase, etc)
Incorporating Spatial Scales into GIS Analysis • Spatial scale is not same as maps scale, rather size relationship. • Studies of Ecosystems • places where life forms and environment interact • structure and function affected by environmental and biological factors including climate, geology, soils and flora
Incorporating Spatial Scales into GIS Analysis • Studies of Ecosystems • hierarchy theory in ecology has emphasized that ecosystems and their underlying biophysical environments occur in a spatial hierarchy, with smaller ecosystems embedded in larger ones • conditions or processes of larger ecosystems can affect or constrain smaller ecosystems
Incorporating Spatial Scales into GIS Analysis • Studies of Ecosystems • For example, logging operations on upper slopes of an ecological unit will likely affect streams and riparian habitats in downslope smaller units. • At the same time pins in a snow-pine forest landscape convert solar radiation into sensible heat, which moves to the snow cover and melts it faster than would happen in a wholly snow covered or wholly forested basin.
Modifiable Area Unit Problem • Modifiable Area Unit Problem (MAUP) addresses the ‘modifiable’ nature of area units used in spatial analysis and the influence it has on the analysis and modeling results. • aggregation is usually stronger correlation, but unpredictable • better to report at different levels
Create Regions • Similar to polygon shapefiles in ArcView • Created in several ways • from existing arcs or polygons • data conversion methods • related table • regions-based commands
Create Regions • Use polygons, not arcs if possible due to common boundaries. • Can be noncontiguous or contiguous • Both function the same but fewer records for noncontiguous • Select polygons and MAKEREGION • Vector Product Format (VPF) imported to ARC/INFO are example of data conversion method.
Create Regions • Create regions by using a related table • Requires subclass in table • REGIONJOIN • Region-based commands • DROPFEATURES, REGIONPOLY • Attribute management • separate, relatable • all.patveg
Regions-Based Query and Overlay • Will not detail • Commands which can perform overlay, query and creation of region subclasses. • Differences in region-based operations • limited to polygon coverages • use logical operations (AND, OR, XOR, and NOT) rather than UNION, INTERSECT, and IDENTIFY • ability to weight influence for snapping
