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I have a large number of points that I need to plot and want to avoid overlaying them wherever possible. Whenever I choose a figure <1 for their size, I don't see any difference, yet ArcMap seems to accept the figure.

Is size '1' the smallest they can be represented?

PolyGeo
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MyFamily
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  • Have you tried exporting to pdf or similar with a size smaller than 1? For lines the difference usually shows better there, but haven't had that small points though. – Martin Nov 26 '14 at 14:52
  • What version of ArcGIS are you using? – artwork21 Nov 26 '14 at 15:46
  • 10.2 (sorry, had to edit the title) – MyFamily Nov 26 '14 at 15:52
  • Part of what you're running into is a screen resolution issue. Points can only be displayed down to a certain size relative to everything else, and sometimes values will fall between two distinguishable sizes and get rounded one way or the other on the screen. Unless you've set your symbology to a fixed scale, no matter your zoom level Arc draws things at the same size - the view is dynamic. If you set a fixed scale (or export to a pdf) the size becomes fixed and gets scaled with zoom, so you may not be able to see a difference unless zoomed way in. – Chris W Nov 26 '14 at 22:11
  • Thanks @ChrisW , can you repost that as an answer? – MyFamily Nov 27 '14 at 09:00

3 Answers3

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The short answer is yes, you can make points smaller than 1.0. There could be a few different things going on:

(1) Are you in map view or layout view? The map data view may be scaling your points so that they appear the same size as you zoom in.

(2) It is very difficult to eyeball the difference between 1.0 and 0.5, for example. On my screen they look the same (both just tiny dots).

(3) Finally, although you may want to display more points, it is worth considering if you should generalize a copy of your data for display. A size of 1.0 points (the measurement, not a point feature) is equivalent to 0.014" (0.03556 cm), also known as 'very small'. I have displayed points down to 0.4 as a test, but would not put this on a map. As a side note, below 0.4 the point disappeared, so maybe ArcMap has a minimum size to display.

You may find these links useful:

Fonts in ArcGIS

Understanding Font Size

Dan
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  • In layout view trying to export. It's hard to tell the difference but I can judge it on the amount of 'black space' in my map (areas where there are no points) - it doesn't change. – MyFamily Nov 26 '14 at 15:41
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    @MyFamily, Later I came across this ESRI article on printing and symbology: "Monitor screen resolution is 96 dpi, so showing .006 of an inch on a 96 dpi screen is not possible..... Anything 1 point or less is shown as the same width, so that it does not disappear." – Dan Dec 08 '14 at 07:03
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    @MyFamily and Dan, that article is somewhat misleading because 96 dpi is not a universal screen resolution. In fact that's actually an OS software setting which can be altered, and true resolution varies from monitor to monitor and depends on size. The article does seem to indicate that ArcMap itself won't display anything less than 1pt on screen, thus you must zoom in to see the difference (0.5pt at 200% = 1pt) as I mentioned in my answer (this only applies to layout view or fixed reference scale in data view though). – Chris W Dec 11 '14 at 18:50
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    Good point Chris. ESRI will display points below 1 pt though, but they disappear at some point. In my case this is at 0.4 pt, but on a 5k screen maybe it would display even smaller points (in layout view, as you mentioned). – Dan Dec 12 '14 at 01:45
  • Sorry, I should clarify my statement. It won't display anything less than 1pt at its true size on screen. Per the article you link, it rounds whatever the value is up to 1pt for display purposes - but as you note only to a certain minimum. As for the '5k' screen, that's where things get tricky. That 96dpi as an OS setting overrides the actual monitor spec. However many real pixels there are in an inch on the actual screen (pixel/dot pitch), they'll be divided by 96 by the OS. But if you have more you can change the OS setting - assuming your eye can make out something that fine. :) – Chris W Dec 12 '14 at 20:29
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The size they are represented is also linked to how big your map is when you are exporting it (assuming you are exporting it) so yes a point can be displayed at less than size 1 but it depnds on what you want to do next.

However if you have a lot of points and reducing the size doesn't help an alternative that might be worth looking into is the Point Density tool. This would allow you to visualise your data in such a way that you don't lose information behind other features. The output is a raster which you can then display to show as a heat map showing areas of high density.

See this answer: https://gis.stackexchange.com/a/42027/14349 and the link it contains for more info: http://blogs.esri.com/esri/arcgis/2010/07/13/spatial-statistics-resources/

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MAJ742
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  • Yes it's for an export, it's just that the map is identical whether the point size is 1 or 0.1 – MyFamily Nov 26 '14 at 15:28
  • Missed this, it must have posted while I was replying. Are the points identical when you export them? Or, they appear identical on your screen)? – Dan Nov 26 '14 at 15:37
  • Both the export and screen, though I'm currently trying @Martin 's pdf approach – MyFamily Nov 26 '14 at 16:06
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Part of what you're running into is a screen resolution issue. Points can only be displayed down to a certain size relative to everything else, and sometimes values will fall between two distinguishable sizes and get rounded one way or the other on the screen. There are only so many individual pixels on your screen with which to draw everything. This effect can also show up when examining lines or graphics at different scales/zoom levels. Particular 'steps' may show jagged lines, odd/uneven hatches, or perhaps not even draw something at one scale only for it to look fine if you zoom in or out a little. This relates both to the screen and the drawing engine of Arc.

Also, unless you've set your symbology to a fixed scale, no matter your zoom level Arc draws things at the same size on the screen - the view is dynamic, so a point displaying at 8pts will be that size at any scale. If you set a fixed scale (or export to a pdf) the size becomes fixed to a reference scale (ie it's 8pts at 1:2000) and then then becomes larger or smaller relative to zoom/scale. In that case you may not be able to see a difference unless zoomed way in. In layout view this effect can be doubled because not only do you have a map scale within the dataframe, but you also have a layout view (page) 'scale' given in percent.

Chris W
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