Some Frequently Asked Questions
And other GIS/Remote Sensing Topics
Can point data in non-GIS formats be used?
Is the dataset a series of points in a spread sheet like EXCEL?
--Add column headings of 8 characters or less.
--Save the data set in a “tab delimited, text” format.
--Use ArcView’s project tool bar, add table, delimited format.
--Use the View tool bar, View/add event theme, choose x and y coordinate columns.
--Use the View tool bar, Theme/convert to shape file, add theme to view.
--Delete from the View the theme created with “add event theme”.
Why won’t a theme display
Are all of the theme’s shape files present? (shape files: *.shp, *.shx, *.shn, *.dbf, *.ndx)
--Minimum files are *.shp, *.shx, *.dbf (* = theme name, i.e. roads, rivers, lakes)
--If a theme cannot be displayed, or the data table is missing, some of the theme’s files may not have been correctly copied.
Is the data set vector (point, line and polygon) or grid/raster/image (grid, row/column, pixel) data?
--Are the proper ArcView extensions active?
Is the dataset in ArcView theme format (i.e. “shape file”) or a supported grid/raster/image format?
--If not, a format conversion needs to be performed.
--Vector conversion can be performed by an import utility/script through AcrView, or an export from the software used to create the dataset. Try to find a format common to both software packages.
--Raster format conversions may require a separate software package.
--This typically happens when the theme’s display properties are set for a specific scale.
--Use the View tool bar, Theme/properties/display, clear any scale settings.
One theme is separated a large distance from the others.
Are the datasets in a common “real world” coordinate system?
--Location, Location, Location!
--The datasets may need to be projected to a common “real world” coordinate system.
What are the “real world” coordinate system parameters of the dataset?
--Check available meta-data.
--Projection (UTM, Albers, Lambert Azmuthal).
--Datum (WGS84, NAD83, NAD27).
--Spheroid (HARN/HPGN, GRS1980, Clarke 1866).
--Meridian and parallels.
--False easting, or westing.
--Units (meters, feet).
What are the “real world” coordinate system parameters of the other datasets?
--The datasets may need to be re-projected to a common “real world” coordinate system.
--Project out to latitude and longitude and then in to new system.
Is the dataset in a geographical/spherical reference system such as latitude/longitude?
--The dataset may need to be projected to a common “real world” coordinate system.
If spherical, are the coordinates in degrees/minutes/seconds (31 30 30) or decimal degrees (31.50833)?
--A dataset in decimal degrees is easily projected to a common “real world” coordinate system.
Why don’t theme positions exactly match?
What was the scale of the dataset’s source material?
--Datasets are created from sources at various relative scales (i.e. 1:1200>1:24000>1:250000)
--Data collected at large relative scales should be more accurate in position.
--Data collected at scales smaller than other datasets may be less accurate in position.
What was the method of data collection?
--Position measurement accuracy varies by method of data collection.
--Some collection methods are: Global Positioning System (GPS), digitizing, hardcopy measurement, aerial photography, digital imagery
--Positions in imagery vary by method of image capture (airplane/satellite/scanner), image resolution, number of control points used for rectification.
Was photo copied material used?
--Photo copied material has distortion.
Ask the University of Florida GIS Librarian:
Answers to other questions may be found at ESRI’s support page:
Answers to FGDL FAQ’s may be found at the FGDL web page: