• SPATIAL DATABASES & MAPPING METHODS •
The various branches of geospatial technology have one thing in common. They originate and/or work with georeferenced data. Georeferencing of data is accomplished through the use of standardized computer file structures called spatial databases. Spatial databases are like "regular" databases in that they contain multiple elements (records) all using the same set of attributes to describe the "what is" aspect of each record. In a spatial database, the "where is" aspect of a chunk of information is expressed in a well-defined numeric addressing system and fused together with the "what is" aspect.
The computer files themselves conform to rigorous standards. The work of building spatial databases from instrument readings and on-the-ground observations is called "mapping".
The job of a database is to store a large amount of data so that it is both accessible and secure.
Spatial databases have to deal with the added complexity of storing spatial information, while maintaining
high levels of capacity, accessibility and security.
New database designs are always being developed because there is continuing demand for data file designs
that are larger, faster and more secure. So folks that are new to geospatial technology not only have to get
a handle on databases (foreign territory for many) and spatial databases (foreign territory for almost everyone).
They also have to become familiar with the many flavors of spatial databases that are in common use:
• Geospatial Technology & Georeferenced Data page on the ottergeospatial.info website.
Authorship and Metadata
A spatial database is an academic and/or technical publication in the same sense as a journal article or reference book. When employing geospatial technology in an academic setting, literature searches should include a critical evaluation of the databases that will be used for reference. Data that is robust enough to use for reference generally comes with extensive authorship and methods information (metadata).
When we employ one of our computer software tools to organize and/or analyze spatially referenced data, we often become authors of one or more spatial databases ourselves. For our work to have lasting value, we need to develop and package it in accordance with published standards. We also need to document our work so that its useablility and robustness will be readily apparent to future users.
The term "mapping" has several connotations. In geospatial technology, we are use it to refer to the integration of spatial references and descriptive information in spatial databases.
|EXAMPLE - Our geospatial data archive contains a "Brown County Street Centerlines" database. Each of the 26,000 records in the database corresponds to a segment of a street and each record furnishes a set of attribute values pertaining to that segment. There are 50 attributes in all - Name1, Name2, Type, SPEED_LIMIT to list a few. In addition to creating a table of attributes for the street segments, the authors mapped the street data - each record contains coordinate pairs that define the location of the street segment on the earth's surface.|
When the author of a spatial database is selecting a referencing scheme, the simplest and most
accurate choice is a geographic coordinate system (one that defines locations in terms of two
angles - longitude and latitude). The earth is a three dimensional solid, why wouldn't
you use a three dimensional referencing scheme? The concept is well-described in the article titled
Latitude and Longitude published by the US Department of the Interior on their
nationalatlas.gov website. Check out the following for more info on this topic:
• Geographic Coordinates page on the ottergeospatial.info website.
It turns out that there are many situations where it is preferable to map data to a 2-dimensional approximation of the earth's 3-dimensional surface. In this case the data author must select an appropriate projected coordinate system. The concept is well-described in the article (pdf) titled Map Projections published by the Michigan DNR. The first page in particular is an absolute gem of concise wordsmithing. Check out the following for more info on this topic:
GPS and GNSS
The US Federal Government's Global Positioning System (GPS) is a powerful data mapping tool. Actually, the old GPS program that many of us are familiar with has been incorporated into the more comprehensive Global Navigation Satellite System (GNSS) program. However the general idea is still the same - estimate location on the earth's surface by measuring distance to fast-moving objects 11,000 miles up. When GPS is used for mapping, locations expressed in latitude/longitude are computed and written to the receiver's memory. Location information recorded by GPS receivers has many uses. Real-time navigation is the GPS function that most of us are familiar with. Once a receiver has estimated it's location on the Earths's surface, it's computer can calculate numeric distances and directions to preprogrammed destinations. More advanced models display navigation information on built-in maps.
At the Biodiversity Center we are more interested in GPS mapping than in navigation. Observers use hand-held receivers to record locations of everything from butterfly sightings to survey markers. Receivers can also be attached to study subjects to allow their movements to be tracked. Yet another use of GPS is the mapping of observations made with portable field instruments. Examples include the integration of GPS with Anabat equipment (used for identifying bat sounds) and digital cameras. Because GPS mapping information often becomes part of the scientific record, the methods used are more rigorous than for navigation.
Marine-Recreation GPS Receivers
The majority of the Biodiversity Center's GPS mapping work is done with marine-recreation receivers. If recommended procedures are used, this equipment is capable of 5-10 meter accuracy. We have around thirty of these units of varying age and technical capability. They are in constant demand for classes and research projects. However, there are usually a few available to be loaned out. Biodiversity Center Program Assistant Kim McKeefry manages equipment sign-outs. About half of our receivers have the Garmin high-sensitivity antenna technology. Anyone planning to work in tree cover should try to get one of these (look for the "x" in the model number).
In spring of 2011, the Biodiversity Center acquired submeter GPS mapping capability. A hardware and software package was purchased that supports positional accuracy down to 50 centimeters. The selected receiver includes several technical advances reported to improve performance in tree cover, which is a known weakness of submeter technology. Biodiversity Center GIS Technician Mike Stiefvater manages sign-out of this equipment. Coaching on the use of the equipment is availble with a little advance notice. Check out our Submeter GPS page for more information on the equipment and how to use it.
GPS mapping work results in latitude/longitude coordinate pairs called waypoints being written to the receiver's memory.
Downloading Waypoints From A GPS Receiver
Raw GPS waypoints are not particularly useful as-is. A number of processing steps are required starting with transfer of the waypoint data to a Windows PC. Check out our downloading options page for more info.