1. Geographic Information
- Levels of Measurement
- Two categories
- Four categories
- Feature Characteristics
2. Sources of Data
- Map Indexes
- On-Line Indexes to Maps and Imagery
Data can be separated into two types or four types. The two categories of geographic data are Qualitative and Quantitative.
Qualitative: Qualitative is: relating to, or involving quality or kind. In this aspect it means geographic data that varies in quality, such as Land vs. Water.
Quantitative: Quantitative is: related to or expressed in terms of quantity or the measurement of. In the terms of geographic data it simply means how much of something there is.
Data can also be divided in four different levels of measurement:
This data is qualitative using labels to describe the differences between objects or data.
Ordinal describes categories or ranks of data, such as the differences between roads on maps or streams on maps.
This sort of data deals with actual numbers on a measurement system without an absolute zero. Such as temperature(on Celsius and Fahrenheit scales).
This data in contrast to interval data deals with an absolute zero. Such as the Kelvin temperature scale and grades.
Continuous data is data that never stops, for example temperature and elevation data is never-ending. Any point in the world where you happen to be there is temperature and there is elevation. In various locations e,levation and temperature are always changing.
Discrete data is well defined or fixed. In all cases of discrete data there always is plenty of it. Some examples of discrete data are the US Census or cows per square mile in Nebraska.
All maps contain geographic features to describe whatever is conveyed on the map but it is feature characteristics that differentiate these features. Which are size, distribution, pattern, neighborhood, orientation, size, shape, and contiguity. Before these features can be used in a GIS system numbers must be assigned to them to be encoded.
For any kind of research there needs to be data to make it believable. There are countless ways of obtaining data from various sources. Since no one wants to get data first hand there are other places look. Some sources are maps or books. Since data is ever-changing one excellent place to obtain up to date current data is the WEB, which houses thousands of online indexes. This is just a short list of the countless sites on the WEB.
This company came on the heels of the Landsat satellite in the early 80's to provide more data to the public. This data, which is very costly upon demand, is very useful in many research options. This data can also be obtained from their online index which is supposed to have less than 5% cloud cover.
ETAK got its started by developing a car navigation system. The system they developed was based on dead-reckoning and did not work well. So ETAK took its very large and very expensive data base and turned it into something profitable. ETAK used Government maps and added information such as one-way streets. Etak became a company providing quality digital road maps and technologically advanced supporting software. EtakMap databases cover the continental United States and Hawaii with feature-rich databases that show single streets ranging from alleys to freeways. These databases also contain addresses, landmarks, parks and water.
The USGS uses DLG's and DEM's to make up quad sheets.(MAPS) DLG's are digital Line Graphs that are vector based maps used to represent roads and streams. Whereas DEM's are rasters based maps that consists of a series of grid squares across a map represented in some cases elevation.
GIRAS or Geographic Information Reporting Analysis System is a Land use, Land cover, Vector Polygon system.
DOQ or Digital Ortho Quad, Digital Ortho photo Quad (Scale of 1:24000) Is a distortion corrected picture of a quad, normally found as DOphotoQ in quarters.
This administration mainly deals with the weather and atmospheric changes. They describe and predict changes in the Earth's environment and conserve and manage the Nation's coastal and marine resources. From this page you can take data from thief various projects. One useful product that they offer is the AVHRR or the Advanced Very High Resolution Radiometry for weather related issues.
From the US Census Bureau anyone can obtain TIGER FILES(Topologically Integrated Geographic Encoding and Referencing). TIGER FILES combined DIME and DLG databases into a seamless map of the US, both urban and rural areas. Every GIS can import TIGER files directly for use.
This governmentally funded organization made all TIGER maps available to download by state, county, city, and various other parameters.
The Nebraska Resource Commission makes all Nebraska geographic data available to download. This data can be imported in ArcView systems.
Submitted by: Derek L. Miller, April 5, 1998. Updated 2008.