topic Re: Find a solution to a practical problem probably involving Buffer in AEC (Architecture, Engineering and Construction) Questions

Find a solution to a practical problem probably involving Buffer

BaranISCEN — Sun, 01 Jul 2018 22:04:22 GMT

#Buffer

Hello,

I have a problem and wanted to share it with the community in order to see if anyone was eventually able to help me finding out a solution. I have actually a dataset composed of points and projected on a shapefile describing European countries.

My goal is the following : create a new shapefile, with zones specified 100 kilometers around the boarders in-between all the States, since I want to see if there are more points close to the boarders, or not.

I thought that Buffer would be a nice way to do it but didn't manage to find out how to practically do this. I converted the polygone shapefile once to line, and then used the function Buffer, but there is nothing appearing. I did the same without converting before.

Thank you very much a lot for your help,

Re: Find a solution to a practical problem probably involving Buffer

DanPatterson_Retired — Mon, 02 Jul 2018 19:42:36 GMT

Do a Select by Location and get all the points that are within the polygons (countries)... keep the selection.

Repeat a Select by Location using the points (with the selection) but use the polylines (boundary) and the "within a distance of option" WITH "select from set (aka selection)"

You should now have the points that fall within the countries that are within X units of its boundary. This would exclude points that don't fall with a country and those that are further from the border than your threshold

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Mon, 02 Jul 2018 22:14:02 GMT

Dear Dan,

Many thanks for your help. Actually, I used "Select by Location" with Select Features from Point with the source layer being by shapefile of european countries. Then I selected the spatial method "are within the source layer".

I created a new layer with the selected points. This time, I used again "Select by Location" with Select Features from "Selected Points" with the source layer being now the Polyline shapefile of european countries. Then I selected the spatial method "are within a distance of the source layer" and put 75 kilometers for the distance, but all the points are always selected.

Do you have any idea ? Thanks a lot

Re: Find a solution to a practical problem probably involving Buffer

DanPatterson_Retired — Mon, 02 Jul 2018 22:18:32 GMT

Was your polyline and your point data in a projected coordinate system?

No point in querying using planar units when your coordinates are in decimal degrees

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Mon, 02 Jul 2018 22:31:20 GMT

Yes, there are both in GCS_WGS_1984 projected coordinate system

Re: Find a solution to a practical problem probably involving Buffer

DanPatterson_Retired — Mon, 02 Jul 2018 22:35:03 GMT

GCS_WGS_1984 is a Geographic Coordinate System with a WGS1984 datum... that is, it is unprojected and the coordinates are in decimal degrees.

Try to find a projected coordinate system that applies to your study area ie a Lambert Conformal conic, and Albers, anything but Web Mercator

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Mon, 02 Jul 2018 22:51:24 GMT

I see. I used Define Projection to put both the points and countries shapefile in a projected coordinate system (the Lambert Conformal conic one). Unfortunately, nothing change. When I select only the points within the continents and then try to find the points that are within a certain distance to the polyline shapefile of countries with borders (source) it still selects all the points

Sincerely sorry to bother you this much and thanks for all

Re: Find a solution to a practical problem probably involving Buffer

DanPatterson_Retired — Mon, 02 Jul 2018 23:16:11 GMT

You never use Define Projection... unless you get a warning that the file has no defined coordinate system.

You must define it back to what it is. then use the

Project Tool...

which is the same tool whether you are in ArcMap or ArcGIS Pro

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Tue, 03 Jul 2018 08:59:32 GMT

Thank you so much! It indeed worked. May I ask why the Define Projection was not appropriate ?

Thanks a lot

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Tue, 03 Jul 2018 09:05:56 GMT

Also, if I may ask one last favor: ideally, I would have liked to exclude the points that are on the seaward side (and therefore not close to a border with another country). Is there any mean to exclude these points and let only those close to another country ?

Re: Find a solution to a practical problem probably involving Buffer

NeilAyres — Tue, 03 Jul 2018 09:15:57 GMT

Because "Define Projection" should only ever be used when you have some data with no defined projection, or when (like in your case), someone mistakenly redefined an existing coordinate system.

Define projection just updates the metadata about the coordinate system of the data but does not actually alter the underlying geometry. To do that you need Project.

Re: Find a solution to a practical problem probably involving Buffer

DanPatterson_Retired — Tue, 03 Jul 2018 11:02:11 GMT

Here is a visual guide...

Define Projection... a Visual Guide

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Tue, 03 Jul 2018 21:28:40 GMT

Thank you very much for this. I had actually a question.

I have a shapefile of the world, at a rather precise level (and sub-divisions) that is apparently undefined (when I add data to Gis). Plus, I have the dataset composed of points (long-lat) undefined also.

Therefore, I just put the two layers but either the first one is displayed or the second one, not both. I then tried to Define Projection by defining them either as World 1984 or a Projected one (Natural Earth) but I can't still display both layers.

Is that related to Define Projection ? Do I have to look in this direction to fix the problem ? Thanks a lot

Re: Find a solution to a practical problem probably involving Buffer

DanPatterson_Retired — Tue, 03 Jul 2018 21:53:44 GMT

Don't use them... or find out what the coordinate systems are before you use the define projection tool.

There must be some metadata with the sources.

If you define something wrong... as my examples in the link show.. is what you get

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Tue, 03 Jul 2018 22:05:14 GMT

Actually, the coordinate system specified in the file attached to the shapefile is World Mercator WGS184. I used the Define Projection with World Mercator. But still impossible to see the points in the meantime - despite the fact that if I add XY the points alone, no matter the definition, they are always displayed.

Re: Find a solution to a practical problem probably involving Buffer

DanPatterson_Retired — Tue, 03 Jul 2018 22:09:48 GMT

World Mercator is a projected coordinate system... if it was defined as such, that is good.

As for the points... if they are in decimal degrees (ie longitude and latitude, with longitude as the X and latitude is the Y) they are probably unprojected and have a

Geographic Coordinate system... like GCS WGS84

They are different...

Re: Find a solution to a practical problem probably involving Buffer

BaranISCEN — Tue, 03 Jul 2018 22:15:27 GMT

If I want to use fishnet later, I have better to put them both in a projected coordinate system? and use Project for the points ?

Thank you very much for all!