GIS Aerial Imagery

Manatee County receives new aerial imagery annually from the South West Florida Water Management District (SWFWMD). SWFWMD negotiates contracts to have imagery collected for each of the 16 counties that comprise the district. These aerial images are then rectified, meaning they are turned into what is called digital orthophotos or orthoimages which lines them up with each other and with what is actually on the ground. Manatee County typically receives the imagery at a resolution of 1 foot per pixel. SWFWMD has provided this imagery since 2003 and continues to provide imagery at yearly intervals.

What is a Digital Orthophoto

An aerial photograph and an orthophoto or orthoimage may look alike, but there are several important differences that allow an orthophoto to be used like a map. A conventional perspective aerial photograph contains image distortions caused by the tilting of the camera and terrain relief (topography) and therefore does not have a uniform scale. You cannot measure distances on an aerial photograph in the same way you would on a map. An aerial photo is not a map.

 

The effects of tilt and relief are removed from an aerial photograph by a mathematical process called rectification. A digital orthophoto is a rectified aerial image.  This means that the image now has a uniform-scale. Since an orthophoto has a uniform scale, it is possible to measure distances directly just as you would on other maps. An orthophoto may serve as a base map onto which other map information may be overlaid. A digital orthophoto quadrangle (DOQ) can be used on-screen to collect, review, and revise other digital data, especially digital line graphs (DLG) and topographic maps. When the DOQ is combined with other digital products, such as digital raster graphics (DRG) or digital elevation models (DEM), the resulting image provides additional visual information for the extraction and revision of basic cartographic information.

 

Applications of Orthoimagery

Orthoimagery supports various geographic information analysis and mapping applications. These data are used to develop and revise vector layers of transportation, cadastral (property), and land use/land cover information. Federal, state, and county agencies use orthoimagery as a base map for wetlands, soil, land parcel, farm-field boundary, forest inventory, and other natural resources mapping, analysis, and planning applications. Benefits of access to public domain orthoimagery include the following:

  • A common and accurate image base map is available for inventories, digitizing, and analyses of many themes of geographic information.
  • Developing geospatial data referenced to accurate orthoimagery facilitates the integration and sharing of data, promotes cooperative processes, and reduces high-cost duplication of database development.
  • Certain data layers of information, such as land cover, are more completely represented on and extracted directly from orthoimagery, rather than from symbolized maps.
  • Users can make accurate distance, areal, and position measurements from orthoimagery.
  • Orthoimages can be combined with digital elevation models for slope, aspect, and three-dimensional analyses.
  • Orthoimagery can be digitally mosaicked, resampled, and merged into a single image of a larger area.

Where to Obtain more Imagery

The South West Florida Water Management District works cooperatively with the Florida State University to provide access to their full collection of imagery through the Florida Images Inventory. The Florida Images Inventory provides downloadable imagery in both Mr. SID or TIFF formats.