Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

[SebastianSalazar]

Hello folks.

In Arc Map 10.1 I have I polyline with distances (2.659542 m) and length (0.00266 km) fields. Those fields were calculated with geomtric calculator.

I am tryin a Multiple Ring Buffer Tool with 30, 50 and 100 metres of distance. At the end, the tool shows 3 rings, however,

2.5 Km polyline is located within the 30 metres ring (see littel blue polyline in inner ring). I am really confused. Why 30 metres ring is larger than polyline length?

The polyline is in WGS 1984 World Mercator.

Can you give an idea(s) to fix this problem?

[DanPatterson_Retired]

your polyline appears to be meters or degrees.  Do not use unprojected data when determining buffers unless you want to calculate geodesic buffers which should be oval.  Project your data if you want to work in Euclidean space

[SebastianSalazar]

Hello Dan. Thanks for your reply

The shp file I am working is in Guatemala. My problem. I don't have the GTM Coordinate System for Guatemala

to define the projection. I spent hours and hours googling, but no succes.

I am not sure how to do your recommendation. Could you help me to define the projection and project the shp?

I enclose the ca-9 shp file.

Thanks againg

[DanPatterson_Retired]

I am not sure, but I will cc the one person who would know...

Melita Kennedy‌

[SebastianSalazar]

Dan. Many thanks.

[MelitaKennedy]

Here's a link to GTM: Guatemala Transversa - IGN‌

• PROYECCION: Transversa de Mercator (tipo Gauss Kruger) en una zona única local.
• ELIPSOIDE: WGS84.
• LONGITUD DE ORIGEN: 90°30' (meridiano central de proyección).
• LATITUD DE ORIGEN :0° (el Ecuador)
• UNIDADES: Metros.
• FALSO NORTE: 0 metros.
• FALSO ESTE: 500,000 metros en el meridiano central.
• FACTOR DE ESCALA EN EL MERIDIANO CENTRAL: 0.9998
• NUMERACI0N DE LAS ZONAS: No esta dentro de la numeración normal de zonas UTM. Se le puede llamar zona 15.5.
• NUEVO SISTEMA DE REFERENCIA GEODESICO: WGS84 preciso, basado en ITRF94 época 1997.5 parámetros del elipsoide

           - semieje mayor 6378137.0 metros

           - semieje menor  6356752.3142,

           - achatamiento = 1/298.257223563.

Below is a well-known text version of the coordinate reference system. Copy it into a .txt file, and make sure it is a single line. Copy the text file and name it gua_ca9.prj. Put it with the other gua_ca9 files.

PROJCS["WGS_1984_Guatamala_TM",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-90.5],PARAMETER["Scale_Factor",0.9998],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

Melita

[SebastianSalazar]

Hello Melita. Many thanks for your help

I did your recommendation. The first time I runned the MRB and nothing happened. Then I checked the code again and I only corrected the word Guatamala for Guatemala.

I runned the MRB againg and the 30 metres ring still displays de polyline. I am confused and not familiar with fixing projection. What I am doing wrong.

Cheer's

[MelitaKennedy]

Hi,

You might try projecting your data to GTM. That will give you a new shapefile/feature class that's projected. Then create the buffers again.

Melita

[SebastianSalazar]

Melita. I really apologyze for my low expertise in Projection.

I tested the shp file with Coordinate System <Undefined>

First from Projections and Transformation I used Project Tool from Feature, but the Input

Dataset or Feature Class diplays the little red x circle. So I close the tool

With Define Projection Tool I selected the shp and in Coordinate Ssytem I selecte GTM. Then I run the MRB and shp file is little in the 3o metres ring

With Create Custom Geographical Transformation Tool. I don't what data I have to enter or select.

I enclose the shp file with Coordinate System <Undefined> including the .txt file from previous message, hoping that you could help me. Please

Thanks againg

[MelitaKennedy]

Hello Sebastian,

I was not very clear in my earlier reply. Use Define Projection to set the geographic coordinate system for your data. It's in decimal degrees. Try using WGS 1984 first (it's in Geographic Coordinate Systems, World). Then use the Project tool to create a new dataset that's in GTM.

Melita

Note: The data could be in NAD 1927 instead.