All About GIS

What is GIS?

Geographic Information Systems (GIS) is an assembly of computer hardware, software and geographic data for capturing, managing, displaying and querying various forms of spatial referenced information. In GIS all information has a geographical or spatial component. GIS is often used as an analysis tool to combine mapping with multiple databases, which in turn allow people to make educated, precise and efficient decisions.

What is the purpose of GIS?

Geographic Information Systems support the following:

  • Visual communication, allowing patterns and anomalies to be quickly identified.
  • Automating activities involving geographic location.
  • Better decision making and planning through querying, mapping, analyzing, & modeling with the whole picture.

Where does the information come from?

The City of Newburgh's GIS obtains spatial-referenced data from a number of sources, including the following:

  • Federal Geographic Data Committee (FGDC)
  • Federal Emergency Management Agency (FEMA)
  • US Department of Agriculture (USDA)
  • US Geological Survey (USGS)
  • US Environmental Protection Agency (EPA)
  • US Fish & Wildlife Service (USFWS)
  • US Department of Housing & Urban Development
  • US Census Bureau
  • NYS Empire State Development
  • NYS Office of Parks, Recreation & Historic Preservation (OPRHP)
  • NYS Office of Real Property Services (ORPS)
  • NYS Department of Environmental Conservation (DEC)
  • NYS Office of Cyber Security & Critical Infrastructure Coordination (CSCIC)
  • Cornell University Geospatial information Repository (CUGIR)
  • NYS Department of Transportation (DOT)
  • NYS Department of Health
  • Orange County Real Property
  • Orange County Water Authority
  • Selected private vendors

Data types range from aerial photo imagery to designated wetland areas. Many of the City-maintained GIS data layers and attributes are created and enhanced internally, such as housing, proposed zoning, building vacant registry, property value, neighborhood, water supply protection zone and landmark.

What is Map Scale?

Scale is defined as the relationship between a distance measured on the map and the true distance on the ground. It can be presented in three different ways:

  • Graphic scale or bar scale
  • Representative fraction ("1/250,000") or ratio ("1:250,000")

What is a Projection?

A mathematically based process for converting locations on the three-dimensional earth surface into two dimensions. Spherical coordinates are converted to planar. Different projections will have different impacts on various aspects of area, distance, and shape.

What is an Orthoimage?

An aerial photograph processed to remove the effect of planimetric shift. It has the correct scale throughout.

What is an Attribute Table?

An attribute table is a database table containing information about geographic features in a GIS dataset. One column typically contains a primary geographic identifier while others might contain additional information. It can often be linked to excel or DBF files as well as PDF or JPG files based on a common ID.

What are some of the common data formats?

Shapefile, DEM, TIFF, Dwg, Sid, Mdb. Many of these formats are binary and therefore readable only with GIS software.

What is Vector Data?

Vector data is the storage of X, Y, and Z coordinates connected to define points, lines, areas, or volumes. They are best suited to store discrete, well-defined data that can clearly be delimited.

What is Raster Data?

Raster data consists of rows and columns of cells where in each cell is stored a single value from 0 to 255. They are characterized by pixel values. For example, orthoimagery, aerial photography, digital elevation models, and digital raster graphic (USGS Topo DRG) are often stored as raster data.

What is a Mapsheet?

A mapsheet is a geographic unit or identifiable spatial area for which one or more data themes are available. Mapsheets are grouped into a spatial series. For example, there are more than 900 7.5 minute quadrangles that include the 62 New York counties as a whole.

What is a GPS?

Global Positioning System (GPS) is a radio emitting and receiving Satellite Navigation System that measures location, velocity and time on earth. Different GPS devices are often used in navigation, mapping, or surveying. For more information, view the Introduction to GIS or the slide presentation slides How GPS Works (475K).

What is Metadata?

Metadata are data about data, used to evaluate digital databases. They document the origin and characteristics of each data set, identification information, data quality, spatial reference, entity, attribute, and distribution.