Rookie on a mission: identify country from latitude/longitude conditionally

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03-01-2016 06:41 AM
MathiasKnudsen
New Contributor

Dear Forum Users,

I'm a rookie, simply stated. I have just about zero experience in using ArcMap. I am, however, writing a bachelor thesis in political science on the impact of earthquakes on regime stability. I have a dataset containing the longitude and latitude coordinates of the epicentre of approximately 13,500 earthquakes scoring more than 5,5 on the Richter magnitude scale. And this is where ArcMap enters the stage: I need to be able to match those coordinates with the country they're placed in. More specifically, to complicate things even further, I need a way of separating the earthquakes on land from those in the oceans as the oceanic earthquakes are out of the scope of the thesis.

Is there any way that ArcMap will let me do this? The end-goal is a dataset where the longitudes and latitudes are converted into countryname with values such as "USA", "Chile", "Oceanic/N/A" or something similar which can be matched with the rest of the variables in the dataset I'm constructing containing year of occurence, magnitude, GDP of the concerned country, regime-type etc.

I hope that I've stated my question clearly enough. Any help is IMMENSELY appreciated!

Best regards,

Mathias Knudsen, University of Copenhagen

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6 Replies
MatthewBaber
Esri Contributor

Good news and bad news.

Bad News: Since this is an academic thesis, you will need to obtain a world boundaries dataset that meets your institution's academic standards for accuracy. This could be more difficult than it appears as borders are controversial and highly disputed topics. I would check with your data stewards as your institution most likely already has an "accepted" world boundaries layer for academic use. Make sure this does not have the exclusive economic zones (EEZ) of countries that protrudes into the ocean.

Good News: The workflow is simple! Using "select by location" you can perform spatial queries. First things first select all earthquakes that fall inside a nation's borders. This will select for all earthquakes inside a land border and therefore exclude all marine earthquakes. With these points selected right click on the layer, navigate to selection, and select create layer from selection. This will create a new layer with just the earthquakes on land. Next, use the spatial join tool to add the fields from the world boundaries to the earth quake points. This will add the countries name (assuming that field is existent in the world boundaries layer) to each earthquake point based on spatial location.

Good luck on your thesis!

MathiasKnudsen
New Contributor

Thank you so much for replying to my question! I think the bad news are manageable once I've had a talk with my supervisor. About the good news: that sounds great! As I'm not experienced with the program, I'll definately need to spend some time delving into the technical details, but that should be manageable as well. Before I invest the time, I would however love to be certain that the approach I have in mind is indeed feasible.

Therefore I have a follow-up question:

Is it possible to a) load data into ArcMap from an excel spreadsheet with earthquake epicentre coordinates (or a similar format); b) pair the coordinates with country-names as described above and c) export the data to an excel spreadsheet that would then have column A: lat, column B: long, and then a column C added with country (or something along those lines)?

I really appreciate the help; thank you so much!

Best regards,

Mathias

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ChrisDonohue__GISP
MVP Alum

Regarding your follow-up question on earthquake data, yes, this can be done with GIS.  One general workflow that could work is this:

1.  Use the Excel data to create an Event Layer and then save as a feature class

ArcGIS Help 10.1 - Add XY data

2.  Spatial Join the feature class to your country layer

ArcGIS Help 10.1 0 Spatial Join

3.  Export to Excel.

ArcGIS Help 10.1 Exporting Tables

Note that step 1 will require some knowledge of projections/coordinate systems and is a place where things commonly can go awry when people first try this.  If this happens, post back here and folks can direct you in how to tackle it.

Chris Donohue, GISP

MatthewBaber
Esri Contributor

HI Mathias,

Yes, this is capable. Chris Donohue, GISP did a great job of outlining the workflow. That will get you what you are after.

Best of luck.

Matt

MathiasKnudsen
New Contributor

Just to follow up: so far things are working out just fine with this - thank you so much for your helpful comments!

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MatthewBaber
Esri Contributor

Really glad to hear it! Don't forget to mark Chris's answer as correct. This will help other people find the answer to this question in the future. Hope to see you around in the future.

Matt

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