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

2. 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

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

4. 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

5. 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

6. 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

7. ENVIRONMENT OF GIS APPLS
Ansar Ali, Ph.D Scholar

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

9. 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

10. 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

11. 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

12. 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

13. 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

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

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

16. 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

17. 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

18. 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

19. Ansar Ali, Ph.D Scholar

20. Ansar Ali, Ph.D Scholar

21. Ansar Ali, Ph.D Scholar

22. Ansar Ali, Ph.D Scholar

23. Ansar Ali, Ph.D Scholar

24. Ansar Ali, Ph.D Scholar

25. Ansar Ali, Ph.D Scholar

26. Ansar Ali, Ph.D Scholar

27. Ansar Ali, Ph.D Scholar

28. Ansar Ali, Ph.D Scholar

29. Ansar Ali, Ph.D Scholar

30. Ansar Ali, Ph.D Scholar

31. Ansar Ali, Ph.D Scholar

32. Ansar Ali, Ph.D Scholar

33. Ansar Ali, Ph.D Scholar

34. Ansar Ali, Ph.D Scholar

35. Ansar Ali, Ph.D Scholar

36. Ansar Ali, Ph.D Scholar

37. Ansar Ali, Ph.D Scholar

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

39. 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

40. 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

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

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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

48. Ansar Ali, Ph.D Scholar

49. Ansar Ali, Ph.D Scholar