ARCMAP-CELL RESOLUTION

[ChuckTurlington]

Hello,

I am using ArcMap 10.2.1.

I am learning about the cell resolution of aerial imagery.  I understand imagery we see from the ESRI World Map Server in ArcMap is composed of many "cells" when zoomed-out in ArcMap.  But the image, when zoomed-in, will eventually arrive at the maximum spatial resolution when the map no longer changes with the zoom, so 1m on the map is equal to 1m on the ground resolution.  Does anyone have a graphic representation of what the resolution cells look like; ie. are they overlapping, or stacked geometrically on a grid, etc. ?

[DanPatterson_Retired]

Moved to Imagery and Remote Sensing place

[NICOLAPEDDIS]

If you alredy know the raster are organized in square cells.

in this case the cells / square pixels of the image have the size of 1 meter per side.

If you continue with the zoom over the maximun will see only pixels but not the objects inside every pixel

That means that this image have a regulal cell grid and every pixel have 1meter in the x dimension and 1 meter in the y dimension.

The cells in a raster image form a regular grid having the geometric resolution in this case of 1 meter

[DanPatterson_Retired]

" 1m on the map is equal to 1m on the ground resolution "

Is not a fixed resolution.  The representation on the ground depends upon the satellite used.  A long time ago, in remote sensing terms, the ground resolution was 30 meters... yes 30m or 900 m2 in terms of area.  Satellites and aerial imagery is capable of much finer resolution now.  In my area, it is possible to get digital aerial photo imagery with a 25 cm resolution when less than a decade ago, it was 2 m (200 cm).  However, with the advances in technology the difficulties in land classification increase since a coarser image does the "averaging" for you and a finer image makes it more difficult to classify a given unit of area on the ground.

[CodyBenkelman · Accepted solution]

Chuck

I'm not certain if you are asking specifically about the cells of the basemaps, or if you're seeking general information about rasters and sell sizes.  If the latter, there are some good graphics here What is raster data?—Help | ArcGIS for Desktop​

If the former, and you're asking specifically about the base maps, the pixels in all of the Esri base maps are defined exactly the same as in Google Maps, Bing Maps, and others, so they are all compatible.  The coordinate system is called "Web Mercator" and was defined to cover the earth with a regular set of tiles that change exactly 2 times in scale as you zoom in or out.   The pixel boundaries are aligned at all levels, so at every level, one pixel is covered by exactly 4 pixels (2x2) from the next higher resolution level.  The original definition for Web Mercator had a maximum resolution of  0.299 meters (actually, 0.29858214164761665) at Level 19, and that is the maximum resolution for the Esri base maps today.  (This will be extended in the near future with special base maps that have higher resolution.)

You can learn more here: Web Mercator - Wikipedia, the free encyclopedia

Note this standard, fixed scale change of 2:1 applies ONLY to the base maps that are stored in a specific format referred to as Raster Tile Cache.  As Dan Patterson points out, different image sources have different resolutions, and especially with UAV (or drone) imagery, we are seeing data now with VERY high resolution (e.g. max resolution measured in a few cm per pixel).  All of this is compatible with ArcGIS but the imagery is not constrained to the fixed scales of the Web Mercator projection.  You may have imagery at 1.0 meter per pixel, or 5 m, or 0.25, or 0.333 or any other full resolution pixel size.

Your statement about "the map no longer changes with the zoom, so 1m on the map is equal to 1m on the ground resolution" is a bit confusing.  ArcMap does not prevent you from zooming in beyond full resolution (unlike the ArcGIS Online web maps which DO stop zooming when you reach maximum resolution).  I think what you mean is "you reach maximum resolution and no longer see improved detail when you zoom in" - instead, you just see larger pixels.

Last comment, if you aren't aware of this, note that all map projections have known & predictable distortions depending on how far you move from the origin of the coordinate system.  As you move away from the equator in Web Mercator, the pixel size becomes less accurate so you need to be cautious about how you make distance or area measurements.   There was a recent discussion about this on GeoNet https://community.esri.com/message/559736?et=watches.email.thread#559736