topic Re: problem when convert a x and y file to a point shapefile in Data Management Questions

problem when convert a x and y file to a point shapefile

PengGao3 — Fri, 03 Apr 2015 21:26:06 GMT

I was trying to convert a group of x and y coordinates into a point shapefile. I use ArcMap 10.2, Here is what I did:

(1) put x and y (in numerical values) in columns in Excel and convert it into a .cvs file;

(2) in ArcMap 10.2, go to file> add data>add XY data;

(3) for coordinate system, I imported the projection of my reference shapefile;

(4) click ok.

(5) export the layer into a shapefile by right click it and go to data>export data;

After I got the shapefile, I realized that it cannot be in line my reference map though both have the same projection. When I check the converted shapefile, I noticed that its EXTENT is different from that of the reference map.

Could anyone tell me what I did wrong and how to fix this problem?

Many thanks.

Peng

Re: problem when convert a x and y file to a point shapefile

SepheFox — Fri, 03 Apr 2015 22:07:23 GMT

It is important that the projection you assign to the x/y points is actually the projection of the coordinates, not the reference file. Do you know what kind of coordinates they are? Are they Lat/Long coordinates? UTMs? Other? Another common mistake, at least here in North America is to forget that coordinates can be negative.

Re: problem when convert a x and y file to a point shapefile

DanPatterson_Retired — Fri, 03 Apr 2015 22:20:41 GMT

In addition to the other comments... people often switch the longitude and latitude values around because of the propensity to say latitude-longitude, thereby screwing up the proper reference to the X and Y axes. And to clarify, only the longitude values in North America will be negative.

Re: problem when convert a x and y file to a point shapefile

SepheFox — Fri, 03 Apr 2015 22:37:25 GMT

Well, that's true for lat/longs Dan, but what about UTMs. Ah, isn't it fun being a coordinate system geek!

Re: problem when convert a x and y file to a point shapefile

PengGao3 — Fri, 03 Apr 2015 22:51:17 GMT

Thanks for you both. I think I got lat/long correct. After conversion, I can see that the converted point shapefile ahs the same projection as the one in the reference map, However, when I go to 'properties' of the converted point shapefile, I noticed that its extent is still based on the original values of lat/long, though there is unit 'ft' at the end of the value. I feel that I may have to do something to make sure that the extent will also be changed to that of the projection I used, but I do not know what to do?

Any suggestion? Many thanks.

Re: problem when convert a x and y file to a point shapefile

SepheFox — Fri, 03 Apr 2015 22:53:33 GMT

Peng, it still sounds like you made the projection match your reference map, instead of whatever they were originally. Is that right?

Re: problem when convert a x and y file to a point shapefile

SepheFox — Fri, 03 Apr 2015 22:54:58 GMT

Can you send a screenshot of what you are seeing in the properties?

Re: problem when convert a x and y file to a point shapefile

SepheFox — Fri, 03 Apr 2015 22:58:50 GMT

If your point x/y values are in lat/long, then you will need to pick geographic coordinates and then choose the correct datum. Here in North America we use usually use NAD 27 or NAD 83, but I'm not sure where you are.

Re: problem when convert a x and y file to a point shapefile

PengGao3 — Fri, 03 Apr 2015 23:01:19 GMT

I think you might be right. I have to go back to check how the lat/long data were obtained. Following is the screenshot. Note at the righ bottom, the unit is still degree though I have already defined the projection for this data.

?[cid:db6044ee-aebb-475f-b084-da05278875ff]

Re: problem when convert a x and y file to a point shapefile

DanPatterson_Retired — Fri, 03 Apr 2015 23:05:18 GMT

actually eastings and northings is the correct way to reference (ie X and Y) and there are no negative values, (the southern hemisphere denotes the equator as 10,000,000m and works down. however, there are many projections where the X value can be -ve depending upon the central meridian used...ie Canada's use of the Lambert Conformal Conic projection which is widely employed by Canadian Governments. the sad thing is that most people don't realize that when you get values in the range +/- 180 and +/-90 you are probably working with a geographic coordinate system and not a projected one

Re: problem when convert a x and y file to a point shapefile

SepheFox — Fri, 03 Apr 2015 23:08:00 GMT

I'm sorry, your screen shot didn't work! If your coordinates are lat/long, then they should be in degree. You would have to REproject to change it to match your other shapefile. Do you see? The program needs to know what the original x/y coordinates are. Once you have made a correctly spatially-referenced shapefile of points, you can use the Project tool to change it.

Re: problem when convert a x and y file to a point shapefile

DanPatterson_Retired — Fri, 03 Apr 2015 23:11:46 GMT

your extent definitely suggests longitude/latitude values and the definition to state plane is wrong. Did you use the Project tool, in the Data Management tools, Projections and Transformations...or did you use the Define Projection tool? If you did the latter, you defined it wrong. When you physically project data you will end up with a new file, if you define it, you just put a suit on a dog...but it is still a dog and nothing has changed it. the procedure is

define the coordinate system of the data...it is either a geographic coordinate system (aka long/lat) or a projected one...that you would have to know...no guessing...find out
once defined, then you can Project the data to get it into the coordinate system you want
this should all be done in a dataframe with no other data in it, because the first file that you add, sets the coordinate system of the data frame and when you project it...nothing will look like it has changed because the 'evil...projection on the fly' takes over and tries to help you.
once projected, open a new dataframe and add the freshly projected data...it will look different and the dog will no longer have a suit on

Re: problem when convert a x and y file to a point shapefile

PengGao3 — Fri, 03 Apr 2015 23:40:19 GMT

?Dan and Rebecca,

It worked !!! Based on what you commented before, I suddenly realized one thing:

the original values of the points are simply lat/long values. When I convert these values into points, no matter what 'correct' projection I will use, it will simply a 'suit' as one of you mentioned on the dog (the lat/long values). This is why the extent of my 'projected' point data shapefile is always based on original lat/long values. The other thing I tried before I posted my question was that when I do the conversion, I did not add any projection. Then, after I convert it into a point shapefile, I define it using the projection of the reference map. It did not work because I noticed that even if I did not add any projection, the extent of the point shapefile is still based on Lat/lomg values. Your comments make me realized one important thing: because the original values are lat/long values, when I convert it into a point shapefile, I should use GCS with appropriate datum! Based on the datum of the reference map, I learned that the correct datum should be NAD 83. So, when I convert the lat\long values into a point shapefile, I used GCS with the datum of NAD 83. After that, I use projection to convert the GCS coordinate system to the one associated with the projection of my reference map. This time, it worked!!!

Many thanks for your help. I hope my summary may help others who have run into the same problem as I.

Thank you again. You made my day!!

Peng

Re: problem when convert a x and y file to a point shapefile

DanPatterson_Retired — Sat, 04 Apr 2015 00:10:46 GMT

you are welcome...and I am sure Rebecca feels the same

Re: problem when convert a x and y file to a point shapefile

SepheFox — Sat, 04 Apr 2015 00:24:38 GMT

Who???

Re: problem when convert a x and y file to a point shapefile

PengGao3 — Sat, 04 Apr 2015 00:26:47 GMT

Sorry if I mass up your name. I mean you! Thanks again for your help.

Peng

Re: problem when convert a x and y file to a point shapefile

SepheFox — Sat, 04 Apr 2015 00:28:00 GMT

It's ok I'm glad we could solve your problem!

Re: problem when convert a x and y file to a point shapefile

DanPatterson_Retired — Sat, 04 Apr 2015 00:31:53 GMT

Seph...you aren't supposed to mark your own comments as helpful...goes against protocol ... could be a glitch but it is showning in the Moderator's view...you should check

Re: problem when convert a x and y file to a point shapefile

SepheFox — Sat, 04 Apr 2015 00:37:27 GMT

Ok, my bad. I thought it would help other people find the answer to the same question. Thanks for letting me know!