Major Areas of Practical Application of GIS Technology vehicle routing and scheduling location analysis, site selection development of evacuation plans Street Network-Based

locating underground pipes, cables balancing loads in electrical networks planning facility maintenance tracking energy use Facilities Management Major Areas of Practical Application of GIS Technology

zoning, subdivision plan review land acquisition environmental impact statements water quality management Land Parcel-Based Major Areas of Practical Application of GIS Technology

forest management habitat, migration routes management wild and scenic rivers preservation recreation resources planning wetland preservation agricultural lands management groundwater modeling and contamination tracking Natural Resource-Based Major Areas of Practical Application of GIS Technology

Data in GIS Using Geographic Data A GIS stores information about the world as a collection of themed layers that can be used together. A layer can be anything that contains similar features such as customers, buildings, streets, lakes, or postal codes. This data contains either an explicit geographic reference, such as a latitude and longitude coordinate, or an implicit reference such as an address, postal code, census tract name, forest stand identifier, or road name. To work, a GIS requires explicit references. A GIS can create these explicit references from implicit references by an automated process called "geocoding," or tying something like an address to a specific point on the earth. Why is data important? To create maps using GIS, you need good data. For example, if you are trying to see the locations of your customers, you will use your database of customer addresses to make that map. You need to ensure those addresses are correct for the map to be useful. Data Types and Models Data for a GIS comes in three basic forms, all of which are demonstrated in the map to the right: Vector data. Tabular data. Raster data.

Basic Data Models (Graphics) There are two types of GIS Data Models: (models used for graphic representation of geographic space) 1.Vector 2.Raster Note: A database structure need seldom be made to suit a data model. But a well prepared data model is vital for a successful GIS analysis.

DATA MODEL OF RASTER AND VECTOR REAL WORLD GRID RASTER VECTOR

Spatial Encoding - RASTER POINT LINE AREA

Spatial Encoding - VECTOR POINT- x, y LINE - x1, y1 - x2, y2. - xN, yN Area (Polygons) - x1, y1 - x2, y2. - xN, yN (closure Point) * a single node with NO area * a connection of nodes (vertices) beginning with a “to” and ending with a “from” (Arcs) * a series of arc(s) that close around a “label” point

Raster Models Quantizes or divides space into discrete packets (cells), each representing a part of the whole Cells are of equal size square, rectangular, hexagon, triangles Loose the ability to represent exact locations (e.g., point represented as single cell) Zero dimensional object rep. with 2D feature Lines represented as a series of connected cells Multiple cells joined at edges or corners, usually with only 1 or 2 neighbors, 1D objects represented in 2D Areas represented as a series of connected cells 2D objects represented in 2D, cells distort area and shape - stairs-stepped appearance

Like the vector data model, the raster data model can represent discrete point, line and area features. A point feature is represented as a value in a single cell, a linear feature as a series of connected cells that portray length, and an area feature as a group of connected cells portraying shape.

Generic structure for a grid R o w s Columns Grid cell Grid extent Resolution

Because the raster data model is a regular grid, spatial relationships are implicit. Therefore, explicitly storing spatial relationships is not required as it is for the vector data model.

Vector Models Features represented in basically the same way as an analog map, permits more precise representation than raster model, permits "empty space”, variations of the vector model Spaghetti models Simplest of vector data structures Does not explicitly store spatial relationships (topology), essentially X,Y coordinates, and which should be connected by lines Doesn’t really "know" if points and connected lines form a line entity or poly entity Topological models Recognizes the concept of an entity Stores spatial relationship information explicitly associated with each entity, most common in GIS

Feature Geometry

Vector Representation

Vector to Raster

Raster Representation

Vector Vs. Raster

PRO AND CONS OF RASTER MODEL pro –raster data is more affordable –simple data structure –very efficient overlay operation cons –topology relationship difficult to implement –raster data requires large storage –not all world phenomena related directly with raster representation –raster data mainly is obtained from satellite images and scanning

PRO AND CONS OF VECTOR MODEL pro –more efficient data storage –topological encoding more efferent –suitable for most usage and compatible with data –good graphic presentation cons –overlay operation not efficient –complex data structure

24 Raster or Vector? While any feature type can be represented using either model, discrete features, such as customer locations, pole locations or others, and data summarized by area such as postal code areas or lakes, are usually represented using the vector model. Continuous categories, such as soil type, rainfall, or elevation, are represented as either vector or raster. C. Tabular data Tabular data is information describing a map feature. For example, a map of customer locations may be linked to demographic information about those Customers Tabular data for use in a GIS can be purchased already packaged with spatial data or it can be found inspatial data your own organization.

Attribute data The “I” in GIS GIS are often split into two components –Coordinate information (describes object geometry or spatial information) –Attribute information (describes other non- spatial properties associate with it) Often referred as tabular data as they are presented in tabular form

GIS data components - spatial & non- spatial Databases - cont. Bolstad, 2005

Attribute Information Presentation DBMSIn GIS, attribute information are typically entered, analyzed, and presented using a database management system (DBMS)

DBMS Functions DBMS incorporates a special set of software tools to manage the GIS non- spatial tabular data –Efficient data storage –Data retrieval –Data indexing –Data reporting

Attribute Tables: Database in ArcGIS Records Fields/Attributes

Selecting the Right Data As you search for data for your GIS, you will go through a process of making a wish list and investigating data that meets your criteria. Following are the most important issues you will need to consider to determine which data you need. 1- What do you want to do with the data? Do you want to draw maps or do a certain type of analysis? Do you want to match customers to street addresses or to telephone exchange areas? Do you simply want to draw an accurate street map, or do you want to use the GIS software to develop delivery routes? Consider carefully how you answer these questions because the answers will likely govern your answers to the following questions. Take into account your medium- or long-term goals as well as those you want to accomplish now. 2- What are the specific geographic features you need? To gain the most understanding from your GIS, determine the level of detail required from your data. For example, do you want all streets or major highways? If so, at what level of generalization—major highways at a "local" scale, such as 1:24,000, or at a "national" scale, such as 1:3,000,000. Even for a seemingly simple feature such as streets, you may need to decide how you want them represented (centerlines, double-lined streets, or connected routes).

31 3- What attributes of those features do you need? Using streets as an example, depending on your goals you will have to determine whether you need none, some, or all of the following attributes: street name, route number, road class, road surface class, address ranges, traffic volume, and under- or overpass. 4- What is the geographic extent of your area of interest? Data can be acquired for areas as small as a ZIP Code or census block or as large as the entire world. You will need to determine the size of the area for which you need data. 5- What is the level of geography you want to examine within your area of interest? Your area of interest can often be broken down into smaller areas. Within a state, for example, you may want to examine statistics by census tract, block group, ZIP Code, or cable TV area. 6- How current must the data be? For some applications, such as land use planning using remotely sensed imagery or aerial photography, obtaining the latest data available is critical. For other applications, data that was collected a year or two before may be adequate. 7- What GIS software will you be using? The answer to this question may affect the data format you select. 8- When do you need the data? Many "off-the-shelf" data sets can be acquired in a couple of business days, but if you need customized data sets, plan ahead. Orders that require customization may take up to several weeks to prepare and deliver. 9- Will you need periodic data updates and, if so, how frequently? Determine if complete replacements of the data are preferred or if you require transactional updates (changes only).

End of Chapter One Thanks 32