- #Datum vs.data how to
- #Datum vs.data professional
How To: Identify an unknown projected coordinate system using ArcMap. If the dataset's extent information appears to belong to a projected coordinate system, refer to the relevant articles below for the user's version of ArcGIS Desktop: Most often, data projected to these coordinate systems have an extent with six to eight digits to the left of the decimal. In the United States, the most commonly used projected coordinate systems are State Plane and Universal Transverse Mercator (UTM). A wide variety of predefined projected coordinate systems, using different units and datums, are installed with ArcGIS. If the dataset's extent information appears to belong to a geographic coordinate system, refer to FAQ: What geographic coordinate system or datum should be used for my data? for more information.īoth GIS and CAD data can be created using projected coordinate systems (PCS). Refer to FAQ: What do the terms geoid, ellipsoid, spheroid and datum mean, and how are they related? for more information about datums. To define the coordinate system for data in a geographic coordinate system, the correct GCS must be selected. The most commonly used datums in North America are North American Datum 1927 (NAD 1927), North American Datum 1983 (NAD 1983), and World Geodetic Survey 1984 (WGS 1984). These data can be created on a vast number of different datums. The graphic below shows the distribution of positive and negative values for longitude (X) and latitude (Y) coordinates worldwide.ĭata with coordinates in decimal degrees are in a GCS. For data in North America, the latitude values must be positive numbers between 0 and +90. For data in North America, the longitude values must be negative numbers between 0 and -180. There are 360 degrees in a circle, so coordinates in DD can never be over three digits to the left of the decimal. These units are often referred to as 'lat' and 'long'.ĭecimal degrees (DD) are angles, and these units of measure are often used with GIS data but rarely with CAD data. Geographic coordinate systems (GCS) use units of decimal degrees for coordinates. Determine which type of coordinate system best matches the dataset's extent information. Save this information for comparison against the properties of Geographic, Projected, and Local coordinate systems as listed below. Ignore any digits to the right of the decimal. Include the minus (-) sign if the coordinates are negative. In the Extent section, note the number of digits to the left of the decimal on the top, bottom, left, and right positions. Right-click the name of the layer, click Properties, and select the Source tab. Click the Add Data button, and add the data with the unknown coordinate system to ArcMap. Examine the coordinate extent of the dataset. Determine which type of coordinate system best matches the dataset's extent information, and visit the related article for that specific type of coordinate system. To identify the correct coordinate system, examine the extent of the dataset. Procedureĭata can be created in one of three types of coordinate systems: #Datum vs.data professional
Refer to FAQ: Projection Basics: What the GIS professional needs to know for more information before proceeding.
#Datum vs.data how to
The instructions provided describe how to identify the spatial reference, projection, or coordinate system of data. Therefore, the coordinate system of the data must be identified and defined. ArcMap's 'project on-the-fly' utility requires that projections be defined so that the data aligns in ArcMap. GIS and Computer Aided Design (CAD) data are frequently received with no spatial reference information. How To: Identify the spatial reference, projection, or coordinate system of data Summary
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