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Arc GIS seems inaccurate for drawing lines of specific length?

BeckyRozumowicz

Hello I have recently been tasked with creating a GIS map of our building layout.

This map needs to be detailed. I need to be able to draw a line that is exactly 10 feet long for example.

I browsed online and saw by creating a verticy and hitting Cntrl L you can tell Arc GIS '10 ft' .

However, if i calculate the geometry of the line this creates via attribute table it seems to always come out larger!

10 ft becomes 12.379 something feet. Why is the calculated geometry always larger? Is there a way to fix this?

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Accepted answers

BeckyRozumowicz

I appears the coordinate system between the data frame and the shapefile were different.

Presuming this was the issue i changed the coordinate system of the data frame to match.

Upon calculation of geometry of something i used Cntrl L on and typed 10 ft for the result was 9.99998

the result for 20 ft was 19.99996. Obviously this minor error is tolerable. Thanks!

All comments

DanPatterson_Retired

by chance are you specifying a horizontal distance but trying to draw a line on an angle?

BeckyRozumowicz

No angles involved. It's all straight lines {unless it is angled and i can't tell on screen, after all, drawing a straight line with a mouse is prone to human error}

DanPatterson_Retired

I rarely digitize, but I keep this link handy for the version I am using ... Keyboard shortcuts that can be used while editing—Help | ArcGIS for Desktop maybe CTRL D for delta x and delta y, atleast you will be able to ensure it is straight

BeckyRozumowicz

Helpful for being 100% sure it is straight, however, even combining Cntrl A {which you can chose direction so, set to 0 for a straight line} and Cntrl L to set length {e.g. 20 ft} when i calculate the geometry it results in ~ 24.## ft [which is 4 feet more than it should be, and the base of my problem...]

DarrenWiens2

Are your layer and data frame in the same projected coordinate system?

MikeVolz

Do you have CAD software where you can draw the features and then export these features in ArcMap to make the map?

BeckyRozumowicz

I'll have to check this.

BeckyRozumowicz

No, we don't have CAD software.

BeckyRozumowicz

Turns out it was the issue, the coordinate system being different.

GregoryElwood1

As a quick, additional note, I set the Map Units and Display Units in Data Frame Properties to Feet. I also use "Move To" (right-click when editing vertices) a lot. You can copy and paste X and Y values to different vertices and make accurate lines and polygons, which can often come in handy when you want to calculate area.

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