On the day of the 9/11 anniversary, I was looking at Google Maps (as you can see – on the iPad). Because I also have the Esri app installed, I went to check out their (and Bing‘s) imagery as well, which led to an interesting discovery that neatly illustrates quality differences between all of these prime mapping services.
As you can see in the images below, there are significant differences for this location (the twin-tower/memorial site). Arguably, the quality level of all three services varies by geographic location (they purchase this imagery from various sources, after all), so my conclusions for this site might be different for other aerial imagery sites. But knowing how many people are interested in New York in general and this site in particular, it is astonishing how little some of the services pay attention to quality. Here’s my opinion of the line-up:
- The imagery is quite recent – judging by the height of the Freedom Tower and the trees on the ground. The memorial fountains were not yet in operation, though.
- Images were taken on a clear day close to noon to minimize the impact of shadows. While there always are shadows from highrises, their impact seems minimal.
- “Building lean” is minimal, too.
If you don’t know this term, “building lean” appears when images are not taken perfectly perpendicular to the earth’s surface. In those cases, sides of buildings are clearly visible and the building “leans” over ground features that may be of interest in the images (e.g. streets).
- Its imagery is also recent and even newer than Google’s. The tower’s geometry indicates that quite a few stories were added between Google’s images and Bing’s. Also, the waterfalls are in operation.
- The images were also taken on a clear day but their timing created deep shadows. Entire streets are dark and features are hard to make out. The overall brightness of the image is also quite low, which might be a problem when viewed in bright light.
- Looking at the Freedom Tower, you can see quite a bit of building lean. You can even see the entire eastern facade and reflections in it. As a result, portions of West St. are completely obstructed. I should mention that this is aerial photography, not Bing’s 45-degree “bird’s eye view”. While the view of the Freedom Tower is impressive, its sides should not be visible like this.
- What is quite strange about Esri’s imagery is that depending on the zoom level, images of differently age get served. The closer zoom levels actually display very old imagery: At one zoom level, the memorials have not even been constructed and the ramp into the “pit” is visible.
- The shadows are also very inconsistent. While one photo has sunlight from the Southeast, another one has it from the Southwest.
- Finally (and again very dependent on the zoom level), there is quite a bit of building lean in some of the images. The least amount actually appears in the oldest imagery. Overall, this effect is not very consistent.
So what is the verdict? Based on image quality and visibility of ground features, Google wins this one hands-down. Google’s imagery is clear, building lean is minimal, and there are no differences between zoom levels.
Bing’s newer imagery is compelling but shadows and building lean make it quite unusable for some purposes.
I am very surprised that the “traditional” mapping company Esri publishes such bad imagery. Zoom levels should show identical imagery, and shadows, building lean and timeliness of the imagery is very inconsistent and in desperate need of improvement. This is especially true for such a high-visibility site like this one.