I am Nancy, new to ArcGIS, and I appreciated anyone's help here!
When I was trying to import Coordinates from Excel into ArcMap, I followed the step from the help menu, it really helped. When it was finished, it shows on the map window (which is shown below). However, then when I add my map (Download from Digimap), it only showed the coordinates, not showing the map. And then I tried add map first, it showed on the map window properly, and then add coordinates, unfortunately, the coordinates are not showing on the map.
Firstly, I checked the coordinates system. They are the same using British National Grid for projected coordinates system and for Geographic coordinate system, GCS_OSGB_1936 are selected as default.
Then, I added data, coordinates and map many times, it gave me same results. It seems that the coordinates could not show on my map.
Thanks for helping!
Solved! Go to Solution.
Under the hood all GPS units use WGS84 geographic coordinates. I am guessing that a coordinate system hasn't been applied to the data when it was imported so ArcMap can't reproject it to match your other map data. Following these steps should resolve the issue:
Open a blank map document in ArcMap then go to File > Add Data > Add XY Data
Click on the Edit button then browse to Geographic Coordinate Systems > World > WGS84. The Coordinate System should now show GCS_WGS_1984.
After the xy-event layer is added to the map you can export it to a feature class by right-clicking on it and selecting Data > Export Data.
Export all features using the same coordinate system as the source data. When prompted add the feature class to the map. If you check the layer properties you will notice that the data has the correct coordinate system assigned:
When you add this data to your other map data ArcMap should be able to reproject your GPS points on the fly to match the coordinate system of your map.
If there are alignment issues you may need to apply a datum transformation within ArcMap or when projecting the data to match your other data.
Those coordinates are lat/long, not British National Grid meters. I assume you want to use a geographic (unprojected) coordinate system (WGS84 or NAD83, probably) to import the points, then Project to British National Grid.
Thanks for your advise here.
I found an example of adding data to ArcMap which is using XY data adding tool box, and it is shown blow.
However, I have no idea how they get XY value, it didnt seems like lat/long.
As Jake pointed out, your data is probably in WGS84 since the units are decimal degrees (and situated in the U.K.). We can further draw this conclusion from Owen's point that the Global Positioning System employs WGS84 for all data collection. Owen provided the exact steps you need to follow for adding your data so I would thoroughly review his post below.
In regard to the sample data you provided, it is in a projected coordinate system, unlike your data, which is in a geographic coordinate system. Geographic coordinate systems employ an angular unit of measure (e.g., degrees of long/lat) for recording location while projected coordinate systems use linear units (e.g., meters, feet, etc.) for recording location. Looking at the number of digits (6) in the sample coordinates, the projected coordinate system most likely has a linear unit of meters. You might chance a guess that it is a UTM coordinate system due to this system's common usage but it could be some other local system that also employs meters or some uncommon UTM derivative. It is possible through trial and error to figure out the correct projected coordinate system for the sample if you know where the points should be but it's always best if you can just get this information from the source.
I would suggest following the instructions provided below by Owen Earley to properly display your points using GCS_WGS_1984 and then reproject them to GCS_OSGB_1936 using the Project tool if needed.
Thanks! After I followed the steps provided by Owen, it works. However, the two layers are in different GCS... It makes me wonder why it works in two different GCS rather than in the same one(previous situation, they are in same GCS).
Then I tried to project the station layer to British Nation Grid, it shows on the map too, but there are some differences between each location which is showing below. I am not sure which one is the accurate results. It would not affect my network analysis results a lot, however, I would like to have an idea why it happened.
Thanks very much!!
It appears to be a datum issue or an improperly defined coordinate system. I tried to reproduce the behavior using the procedure suggested for this discussion but everything worked correctly. A few questions:
1 What is the coordinate system of the data frame (GCS and if used, PCS)?
2. What, if any, transformations are being used for the data frame? If there are multiple GCS's being transformed to the data frame GCS, then list each GCS and its transformation.
3. What is the coordinate system of Export_Output_3? Check the layer's properties to verify it is what you think it is.
4. When you projected Export_Output_3_Project to British National Grid, what geographic transformation did you select?
There are a variety of things that can go awry when bringing in X,Y data. Some suggestions:
Data preparation / advice:
1. ArcMap sets the coordinate system based on the first layer added. It is usually best to add the known data before bringing in the unknown data (in your case, the GPS data).
2. Oftentimes what goes awry when bringing in GPS data is that the GPS data was collected in a different projection/coordinate system than your base data. It can be converted to the same coordinate system as your base data, but you will need to know precisely which system it was originally collected in so the correct conversion can be done.
3. Another aspect that comes into play is how data gets read into ArcGIS from Excel. Excel is not always read cleanly by ArcGIS, so it is best to do some cleanup of the Excel data beforehand. First, make sure the field names don't have spaces or restricted characters. Second, define the fields explicitly instead of leaving them as "General". For example, for attribute text, highlight the field, select Format Cells, and then select "Text". For numbers, select "Numbers" and make sure the "Decimal Places" is set appropriately.
1. After checking the above, bring in your data again. First bring in the known layers, then the GPS data. If the GPS data is not showing up where expected, you need to troubleshoot it.
2. If it is only slightly off, the Datum may be incorrect. For example, here in California we have about a 80 meter shift in the data when it is mis-assigned from a NAD27 to NAD83 datum.
3. If the GPS data lands across the world from where you expect, there are is a major coordinate system issue.
- When bringing in the data, was the Geographic Coordinate System explicitly defined when bringing in the data when given the option to choose a coordinate system?
- In some parts of the world the Coordinates in GCS are negative. Did the negative sign get left out?
- If the GPS data is in Decimal Minutes (DM) or Degrees Minutes Seconds (DMS), it needs to be converted to Decimal Degrees (DD) before it can be brought into ArcMap.
Also, here's a link to an article on importing data which may help:
Chris Donohue, GISP
As Jake mentioned, getting a look at an example of how the coordinates are stored in the table would be helpful. In addition to what has already been suggested by Chris, have you tried swapping the two fields you are specifying for the X and Y coordinates? This is a common mix up.