Before starting any analysis, one needs to assess the problem and establish an objective. It is important to think through the process before making any judgments about the data or reaching any decisions; ask questions about the data and model; and generate a step-by-step procedure to monitor the development and outline the overall objective. The following steps outline the basic procedure for geographical analysis:

  • Establish the objectives and criteria for the Define the problem and then identify a sequence of operations to produce meaningful results.
  • Prepare the data for spatial operations. Prepare all map coverages for the proposed data Add one or more attributes to coverages in the database if necessary.
  • Perform the spatial Perform the spatial operations and combine the coverages, e.g. creating buffering zones around features, manipulating spatial features and performing polygon overlay.
  • Prepare the derived data for tabular Make sure the feature attribute table contains all the items needed to hold the new values to be created.
  • Perform the tabular analysis. Calculation and query the relational database using the model defined in step 1.
  • Evaluate and interpret the Examine the results and determine whether the answers are valid. Simple map displays and reports can help in this evaluation.
  • Refine the analysis if needed and repeat the analysis.

Types of GIS Analysis

Spatial measurements

GIS makes spatial measurements easy to perform. Spatial measurements can be the distance between two points, the area of a polygon or the length of a line or boundary. Calculations can be of a simple nature, such as measuring areas on one map, or more complex, such as measuring overlapping areas on two or more maps.

Information Retrieval {or selection}

 With a GIS we can point at a location, object, or area on the screen and retrieve recorded information about it from the Database Management System (DBMS) which holds the information about the map’s features.

In order for a GIS to answer the question "what is where?" we need to carry out retrieval or selection. "Geographic search or selection is the secret to GIS data retrieval" so GIS systems have embedded DBMSs, or link to a commercial DBMS.

a) Searches by Attribute {or selection by Attribute}

 Most GIS systems include as part of the package a fairly basic relational database manager, or simply built on the exiting capabilities of a database system. All DBMS include functions for basic data display. Searches by attribute are then controlled by the capabilities of database manager.

Find is the basic attribute search. Find is intended to get a single record. Find can be browse or by searches. Examples include show attributes, show records, generate a report, find, recode, select, renumber, sort, compute allows the creation of new attributes based on calculated values, restrict, join, replace; all are examples of data reorganization.

Attribute queries are not very useful for geographic search as they don’t or difficult to indicate location; so they just work as humble assistants in our geographical searching needs.

b) Searches by geography {or spatial selection}

Spatial selection is to extract specific features based on their location. The form of select used most is buffer operation. Buffering is a spatial retrieval around points, lines, or areas based on distance

c) The query interface {or Query}

The user must interact with the data in an appropriate way, to do that, we need the query interface. Most GIS packages are fully integrated with the WIMP (windows, icons, menus, and pointers) and use the GUI (graphical user interface) of the computer's operating system, such as windows to support both a menu-type query interface and a macro or programming language. And the fairly recent trend is that most GISs also contain a language or macro tool for automating repetitive tasks; e.g. ArcView's Avenue, MapInfo’s MapBasic, and Arc/Info's AML

SQL (standard query language) has been developed to be a standard interface to relational databases and is supported by many GISs. These user interfaces have specific characteristics.

Spatial overlay

One basic way to create or identify spatial relationships is through the process of spatial overlay. Spatial overlay is accomplished by joining and viewing together separate data sets that share all or part of the same area. The result of this combination is a new data set that identifies the spatial relationships. Spatial overlay allow combining two or more (different) layers and applying the set-theoretic operations of intersection, union, difference, and complement

Boundary analysis

Boundary analysis, which is often referred to as districting, helps define regions according to certain criteria. This procedure is used to define area of specific demographic characteristic for example. Since districting is normally an iterative process involving the development of numerous scenarios based on various combinations of desired criteria, the computing power of the GIS proves to be a real timesaver. Rather than struggling with paper maps and adding machines, it is able to interactively define proposed boundaries

Buffer analysis

 Buffer analysis is used for identifying areas surrounding geographic features. The process involves generating a buffer around existing geographic features and then identifying or selecting features based on whether they fall inside or outside the boundary of the buffer.

This process is used to identify neighborhood.

Neighborhood Operations

Neighborhood operations can evaluate the characteristics of the area surrounding a specific location: Neighborhood functions operate on the neighbouring features of a given feature or set of features (location (s)).

  • Search functions allow the retrieval of features that fall within a given search window (rectangle, circle, or polygon).
  • Line-in-polygon and point-in-polygon functions determine whether a given linear or point feature is located within a given polygon, or they report the polygon(s) that a given point or line are contained in.
  • Topographic functions compute the slope or aspect from a given digital representation of the terrain (digital terrain model or DTM).
  • Interpolation functions predict unknown values using the known values at neighboring.
  • Contour generation functions calculate contours as a set of lines that connect points with the same attribute value. Examples are points with the same elevation (contours), depth (bathymetric contours), barometric pressure (isobars), or temperature (isothermal lines).

Connectivity Operations

Connectivity functions involve traversing an area and accumulating values: Contiguity measures, Proximity, Network functions, and Visibility functions

  • Contiguity measures: evaluate characteristics of spatial units that are contiguous (are connected with unbroken adjacency). An example would be the search for a contiguous piece of forest of a certain area and
  • Proximity functions: The best known example of a proximity function is the buffer zone generation (or buffering).
  • Visibility functions: are used to compute the points that are visible from a given location (viewshed modeling or viewshed mapping) from a digital terrain
  • Network Analysis: Network analysis is used for identifying the most efficient routes or paths for allocation of services, and for evaluation of it. Identifying an efficient route or path is finding the shortest or least-cost manner in which to visit a location or a set of locations in a network. GIS can handle complex network problems, such as road network analysis. A GIS can work out travel times and the shortest path from A to B. This facility can be built into more complicated models that might require estimates of travel time, accessibility or impedance along a route system. Network analysis can also be used to optimize the allocation of resources. Such allocation is performed by identifying and creating areas of influence or service zones based on certain criteria. It is accomplished by assigning portions of a network to a location based on impedance.

Digital Terrain Analysis

GIS can build three dimensional models, where the topography of a geographical location can be represented with an x, y, z data model known as Digital Terrain (or Elevation) Model (DTM/DEM). The x and y dimensions of a DTM represent the horizontal plane, and z represent spot heights for the respective x, y coordinates.

Network (TIN):- The data sets derived from a Digital Terrain Model can be used to analyze environmental phenomena or engineering projects that are influenced by elevation, aspect or slope. The visualization (display) power of the computer allows the terrain data to be visualized in three-dimensional form, often from any angle of view (this is known as point-of-view analysis).