Graphical Locater Home Page

Key Words: Graphical Locator, point-and-click position data, USA maps, state maps, HUC region maps, custom maps, township-range-section (TRS) conversion, UTM conversion, degrees-minutes-seconds (DMS) conversion, HUC maps and information.

Quick Instructions

Most users will go straight to the default Graphical Locater starting map (also linked as "USA map" in the lead image), or to one of the other starting maps, and then select an area for a more detailed map. On the more detailed map, you may move to adjacent maps or get information for any location by clicking on it. You may "zoom on that location" to see more detail or use the "Back" button on your browser to return to the map. Many users will find it convenient to cut and paste Graphical Locater results into other files. If you need more information come back to this page and read on.

Introduction

I designed Graphical Locater as an aid for acquiring and refining location data and related measures. The main graphical interface is useful only for people who recognize the position of interest when they see it on the maps. Some users will find it useful to follow along on printed maps that they are more familiar with.

News

June 7, 2013. Following the death of Daniel Goodman and my retirement, Graphical Locater is now officially abandoned after serving 31,287,393 location requests. The program and its server will be left running under the care of the MSU ecology department until something breaks. Users are encouraged to find replacement services that are under active maintanence. There is an archive for some of the old news

Area of Coverage

The Graphical Locater program is currently limited to the Northwest Quarter of the Earth, that is, 0 to 90 degrees north latitude and 0 to 180 degrees west longitude. The results, however, are very limited outside the area of the USA. For any location, Graphical Locater always does the best that it can with data that are available. Complete Graphical Locater results are available for the conterminous USA, except that legal descriptions are limited to the states covered by trs-data. The state of Hawaii, as well as Puerto Rico and the Virgin Islands have normal map coverage and mostly complete result pages (no identification of state, county, HUC, or Omernik ecoregion). The state of Alaska lacks the 1:100,000 cell maps and has a similar result page.

Graphical Locater Starting Maps

The Graphical Locater starting maps, or level 1 maps, are linked to level 2 maps by an appropriate image configuration file. There are currently 4 starting map areas, the conterminous U.S.A with many versions, the Greater Montana Area (the original area for Graphical Locater), Puerto Rico and the Virgin Islands, and Hawaii. There is a page that gives the color scheme for Graphical Locater Maps. The conterminous U.S.A maps are based on the area, projection and data of the very useful Conterminous U.S. AVHRR project. I reduced the final image size to 1152 by 725 pixels to fit on at least some screens. You can measure your viewable screen size (in pixels) here.

Graphical Locater Level 2 Maps

The level 2 maps are linked to the Graphical Locater program that returns information for any location. These maps are always pixel-centered maps of straight latitude and longitude. Square pixels are nice, but not required. There are several types of level 2 maps. There is a page that gives the color scheme for Graphical Locater Maps.

Returned Information Details

  1. Latitude/Longitude: The location data in decimal degrees of arc with the degree symbol and hemisphere (North and West). Four decimal digits translates to less than 10 meters. The output is also given as degrees (°), minutes(') and seconds ("), the last has 1 decimal digit. Decimal minutes is the seconds divided by 60 added to the minutes.

  2. The legal description: This includes, in order, the meridian, township, range, section and state. This program has this information only for the western states. Note that township, range and section define an unique square mile only when the meridian is also given.

  3. UTM: This is the Universal Transverse Mercator zone and x,y coordinates in meters. This conversion is done using the Geodetic Reference System of 1980 (GRS 1980) of the North American Datum of 1983 (NAD 83). Many projects are still using the Clarke Spheroid of 1866 of the NAD 27. Note that a UTM coordinate is meaningless unless the zone is also reported. The UTM coordinates can be used to calculate the distance between to points, as long as the zone is the same.

  4. The pixel size: This is given only for entry from a clickable map. The first value is for the E-W direction and the second for the N-S direction to the nearest meter. This is a measure of the expected accuracy. Distances are based on the GRS80 ellipsoid. Non-square pixels are the result of map distortion in the North-South direction. Map distortion does not affect location accuracy, except for the change in pixel size.

  5. The distance from the marked point: This is given only for custom maps which already have 1 point defined. Distances are based on the GRS80 ellipsoid and reported to the nearest meter.

  6. The elevation: The height above mean sea level in meters and feet. This is based on simple bilinear interpolation of the original 1-degree (3 arc second) digital elevation model (DEM) data. The median absolute difference between Graphical Locater elevations and the elevation reported for over 30,000 named places in the us_concise file of the GNIS was 5.5 meters. Of the 10 largest errors, all were in the name file. As with all grid interpolations, the elevation of peaks will be low and the elevations of dips will be high. The local roughness gives some measure of the point elevation uncertainty.

  7. The gradient: This is the maximum slope through the point. Slope is feature of a line, not a point. The gradient is calculated from the X-direction slope and Y-direction slope. The directional slopes are based on bilinear interpolation of elevation over a radius of 35 meters. The reported gradient is thus a very local measure (about 1 pixel on the standard maps). Any location within 1 arc second of a whole degree cell edge is moved slightly inward to prevent the need to bridge across the DEM units and the discrepancies that occur there.

  8. The aspect direction: This is the direction of downhill gradient. I am using 0 for North, 90 for East, 180 for South and 270 for West. The standard abbreviation of the 8 compass directions is given after the number value. Note that this is a circular statistic with 359 and 1 being almost the same, true North. The aspect calculation is based on the X-direction and Y-direction slopes. The directional slopes are based on bilinear interpolation of elevation over a radius of 35 meters. The reported aspect is thus a very local measure. Any location within 1 arc second of a whole degree cell edge is moved slightly inward to prevent the need to bridge across the DEM units and the discrepancies that occur there.

  9. The local roughness: This is simply the standard deviation of surrounding elevation values. This calculation uses the nearest 16 elevation values in the original 1-degree (3 arc second) digital elevation model (DEM) data. This corresponds to a radius of about 125 meters. Multiple 1-degree units are never combined for this calculation to avoid the discrepancies that occur there. Variation in elevation is only 1 of 3 components of terrain roughness. Variation in gradient and variation in aspect are too demanding to calculate here. The local roughness interpretation is based on almost 100,000 equally spaced points across the USA. Flat is for no variation in elevation; slight is above zero and below the 25th percentile, average is between the 25th and 75th percentiles, moderate is between the 75th and 95th percentiles and extreme is over the 95th percentile.

  10. The location (X, Y; Z): This is my choice for standard data entry, many others are possible. West longitudes are negative and X (longitude) comes before Y (latitude).

  11. The state, county and FIPS code: This determination is based on a 850 m raster grid created from 1:2,000,000 DLG data. It will be a little "rough on the edges". A test run against the GNIS gave the error rate at 3.16%, but some of the errors are in the GNIS. Many of the errors are named peaks that occur on the county line.

  12. The hydrologic unit name and code: These are the USGS 8-digit HUC composed of 4 2-digit codes that give the region, subregion, accounting unit and catalog unit. The "Place point in HUC" link allows you to mark the current position in the current HUC map. The HUC determination is based on a 850 m raster grid created from the 1:2,000,000 DLG data that were further refined in our lab. Our refined version should match the USGS intent, except for California subregion 2 accounting unit 1 and subregions 3 and 4. In these areas, some units were constructed so poorly that they have no utility for our purposes and they were restructured to better match drainage borders. The HUC is linked to our own HUC summary page that features 3 graphical locater maps for each unit. Because of the grid size, the HUC determination will be a little "rough at the edges". A test run of almost 1000 sample sites in one of my projects, gave the error rate at 0.85 %. It also discovered one error in my data! Most errors occur at the edges of the units (mouth or headwaters) and these can be easily double checked by selecting a more central location.

  13. The Omernik ecoregion name and number: These are the 76 regions used by Omernik, 1987 for the conterminous United States. The more or less typical flag is also given. The ecoregion determination is based on a 850 m grid and will be a little "rough at the edges". The error rate should be similar to that of the HUC and FIPS determination, but I have no independent data to check.

  14. The 1:100,000 map: This is a link to the Graphical Locater 1:100,000 map without checking to see if that map exists.

  15. Zoom on that location: This is a link to the Graphical Locater map making program at will make a large-scale (small area) map centered on the selected location. If there are no data within that area, you will get a blank map.

  16. Switch to TerraServer: This is a link to Microsoft's TerraServer centered on the selected location.

  17. Nearby named places: These are from the Geographic Names Information System (GNIS). Linear features are split into "mouth" and "head" points. The state and county names replace the original FIPS codes, except for "head" locations. Here, the state and county might be wrong, so they are left out. I converted the position data (X,Y as decimal degrees of arc) from NAD 27 to NAD 83 to be more comparable with the TIGER/LINE 1995 line data. The elevation, if given, is the original GNIS data in feet. The distance from the selected location is based on the GRS80 ellipsoid. Selecting the position of a named place makes it the current Graphical Locater position and it allows zooming on that position exactly (or within a few meters due to rounding).

  18. The 7.5 minute series topographic maps for that area: This is based on the map names part of the Geographic Names Information System (GNIS). The map names are in a 3 by 3 table similar the "adjoining map table" on many printed maps. The top is North and right is East. The selected point is on the map that is named within the middle cell.

Accuracy

The positional accuracy of Graphical Locater is limited by the pixel size (reported with every location), the users aim (unknown), and the underlying map data (+/- about 50 meters for the 1:100,000 map data). The program introduces no error of its own, as far as I know. Graphical Locater results are better than any other method available to me, so I have no way to independently test its accuracy, others are invited to do so and report back.

Base Data

Base Programs

The Graphical Locater project has 4 main programs or interfaces:
  1. GL - handles all level 2 clickable maps.
  2. XY-data - handles form inputs of longitude & latitude and includes forms for degrees minutes and seconds and UTM coordinates.
  3. TRS-data - handles form inputs of township, range and section.
  4. XY-info - provides an full result page for a known longitude and latitude.
Most of the code is common to all 4 programs and most of it is original code in FORTRAN. The following code and programs are not original.

Acknowledgments

The U.S. Geological Survey deserves much credit for making massive amounts of useful mapping data and programs freely available. Martin Wefald very kindly made his most useful trs2ll program available to handle the township-range-section conversions. Mike Ivie, here at MSU-Bozeman has offered many suggestions on this project. Allen Porter with the Information Technology Center at MSU-Bozeman has helped with many programing issues from the start of the Graphical Locater project. Lisa Bogar also with the Information Technology Center, keeps the servers up running. Much of the upgrades to Graphical Locater were funded by the U.S. Fish and Wildlife Service to help support the National Wild Fish Health Survey.
1995 OCT 30, last updated on 2007 JAN 03; D.L. Gustafson