GIS MAP OVERLAY ANALYSIS Ansar Ali Ph.D Scholar Ansar Ali, Ph.D Scholar

INTRO Geographic Information System (GIS) play a key role in real life as they are essentially spatial in nature A map with a database behind it. A virtual representation of the real world and its infrastructure. A consistent “as-built” of the real world, natural and manmade Which is Queried to support on-going operations Summarized to support strategic decision making and policy formulation Analyzed to support scientific inquiry Ansar Ali, Ph.D Scholar

Geographic Information System Data Management Geographic Information System Science Decisions Ansar Ali, Ph.D Scholar

What is GIS A method to visualize, manipulate, analyze, and display spatial data to study the world “Smart Maps” linking a database to the map, creating dynamic displays Ansar Ali, Ph.D Scholar

Why GIS GIS technology has evolved to help us process info about place and put it in a context that allows us to act. Actually extending our minds by abstracting our world into the knowledge objects that you create and maintain data, imagery, models, maps, and applications. GIS is facilitating a systematic framework for knowing, and our shared work is leading to a collective understanding. Ansar Ali, Ph.D Scholar

EVOLUTION OF GIS 1969 – 1980 : Computer Mapping that yielded to Spatial Data Management The 1990s centered on GIS Modeling (analysis focus) In 2000s Web sol was introduced Today, GIS is centered on Multimedia Mapping (mapping focus) Ansar Ali, Ph.D Scholar

ENVIRONMENT OF GIS APPLS Ansar Ali, Ph.D Scholar

MAP OVERLAY ANALYSIS Ansar Ali, Ph.D Scholar

GIS OVERLAY ANALYSIS A map with a database behind it. A virtual representation of the real world and its infrastructure. A consistent “as-built” of the real world, natural and manmade Which is Queried to support on-going operations Summarized to support strategic decision making and policy formulation Analyzed to support scientific inquiry Ansar Ali, Ph.D Scholar

GIS OVERLAY ANALYSIS Geographic Information Systems (GIS) model selected aspects of reality. Overlay analysis is one of the spatial GIS operations. Overlay analysis integrates spatial data with attribute data. (Attributes are information about each map feature.) Overlay analysis does this by combining information from one GIS layer with another GIS layer to derive or infer an attribute for one of the layers. At its simplest, overlay analysis can be a visual operation, but analytical operations require one or more data layers to be joined physically. Ansar Ali, Ph.D Scholar

GIS OVERLAY ANALYSIS This overlay, or spatial join, can integrate data of different types with assessor's parcels such as: Soils Vegetation Land ownership Jurisdictions, etc.. Ansar Ali, Ph.D Scholar

GIS OVERLAY ANALYSIS Storing digital data in multiple "layers" is not unique to GIS, of course; computer-aided design (CAD) packages and even spreadsheets also support layering. What's unique about GIS, and important about map overlay, is its ability to generate a new data layer as a product of existing layers. In the example illustrated Ansar Ali, Ph.D Scholar

Map Overlay Map overlay combines the geometry and attributes of two feature maps to create the output. Must be same coordinate system and zone, same datum. Multiple combinations as a process. Ansar Ali, Ph.D Scholar

Overlay Functions: Overlays of two feature classes creates a new feature class with attributes from the two originals... Ansar Ali, Ph.D Scholar

What kinds of analysis can we do with GIS? Ansar Ali, Ph.D Scholar

Vector Overlay-Point-in-Polygon Point-in-Polygon is used to find out the polygon in which a point falls. Example: Which landcover does each meteorological station fall into? Why is there a problem in the alternative order – polygon to point? Ansar Ali, Ph.D Scholar

Vector Overlay-Line-in-Polygon Used to find out what polygons a line falls within. More complicated than point, because one line can be in more than one polygon Example: Which roads pass through forest areas? What parcels might be affected by a new bike trail design? Ansar Ali, Ph.D Scholar

Vector Overlay- In ArcMap Arc Toolbox Available Functions: Union – “Atbox-An Tools-Overlay-Union” Intersect – “Atbox-An Tools-Overlay-Intersect” Clip (“cookie cutting”) – “Atbox-An Tools-Extract-Clip” Merge – appends two or more layers together to create a new layer (e.g., side by side). “Atbox-Data Management Tools-General-Append” Dissolve – reduces number of features by merging adjacent features with the same attribute value. Creates a new layer. “At box-Data Management Tools-Generalization-Dissolve” In ArcMap – all under Geoprocessing menu Ansar Ali, Ph.D Scholar

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Error Propagation in Map Overlay Ansar Ali, Ph.D Scholar

Careful because tolerance combines all values that are SLIVERS Sometimes when layers represent similar shaped boundaries, they don’t match perfectly due to scales variations between the two data sets (e.g., counties map vs state map outer edges. This is an artifact and not real so those slivers can be corrected by using a tolerance setting. Careful because tolerance combines all values that are close, not just the ones you want Sometimes slivers are real... It is difficult to determine at times if they are real or not Ansar Ali, Ph.D Scholar

Dissolve takes polygons that are adjacent or overlap (BEFORE) and uses attributes within each that are identical to create larger polygons (AFTER) Ansar Ali, Ph.D Scholar

Buffers around roads creates a mess... Until you dissolve the boundaries between the various buffer zones created Ansar Ali, Ph.D Scholar

Append- tables must match precisely before applying A tool used to combine features of two or more layers into a single new feature of the same class Map of Polygons 1 + map of Polygons 2 = new map layer of combined Polygons Merge is very similar, except that it allows the user to specifically determine what attributes fields to include rather than insisting that the table match exactly. Its more flexible than the append tool Ansar Ali, Ph.D Scholar

Raster Overlay- In ArcMap “Map Algebra” or “Mapematics” Two raster layers with same cell size can add, subtract, multiply, divide them to produce a new layer In ArcMap: Spatial Analyst extension, “Raster Calculator” Ansar Ali, Ph.D Scholar

Network Analysis Networks are sets of interconnected lines through which resources can flow. E.g., roads, rivers, powerlines Concept of “Impedance values” (attributes of line segments such as speed limits of roads, etc) Classic networking problems: Shortest path Traveling salesman problem (visit many locations in a day – what is the quickest route to them all?) Ansar Ali, Ph.D Scholar

Network Analysis Location-Allocation modeling (e.g., matching supply of services with demand through a road network) Route tracing (ability to trace the flow of goods, people, services or information through a network of lines) ArcGIS - Network Analyst extension Ansar Ali, Ph.D Scholar

Surface Analysis Contour Slope Aspect Hillshade Visibility analysis… (“Viewshed” in ArcMap) In ArcMap Spatial Analyst extension, “Surface analysis”; Also in 3-D analyst. Ansar Ali, Ph.D Scholar

Other ArcGIS Spatial Analysis Functions Hydrologic Analysis Density mapping Multivariate statistics (e.g., classification,principle component analysis ,3 Dimensional visualization/city planning.) Ansar Ali, Ph.D Scholar

Ansar Ali, Ph.D Scholar

Ansar Ali, Ph.D Scholar