如图，把三个大小相同的正方形甲，乙，丙放在边长为9的大正方形中，甲与丙的重叠部分面积记为S1，乙与丙的重叠部分面积记为S2，且均为正方形，正方形甲、乙一组邻边的延长线构成的正方形面积记为S3，若S1 - S2 = 2S3，且S3 = 1，求图中阴影部分的面积。---**Extraction Content:**
**Part 1: Individual Squares**
- Three separate square shapes are depicted.
- One square is labeled "甲" (Jia) inside.
- One square is labeled "乙" (Yi) inside.
- One square is labeled "丙" (Bing) inside.
**Part 2: Composite Geometric Figure**
**Chart/Diagram Description:**
* **Type:** Geometric Figure / Area decomposition diagram.
* **Main Elements:**
* **Shape:** A large outer square boundary. Inside, the area is partitioned into multiple regions by horizontal and vertical lines. There are also smaller square and rectangular shapes within the central area.
* **Lines:** Internal horizontal and vertical lines divide the large square. These lines intersect off-center.
* **Labels:**
* A large region in the bottom-left of the large square is labeled "甲".
* A large region in the top-right of the large square is labeled "乙".
* A large region in the bottom-right of the large square is labeled "丙".
* In a central area, there are smaller labeled regions:
* A square labeled "S₃" is located in the center of this cluster.
* A rectangle labeled "S₁" is located immediately to the left of S₃.
* A rectangle labeled "S₂" is located immediately above S₃.
* A region (appears rectangular) labeled "丙" is located immediately to the right and below S₃. (Note: This is a smaller region labeled "丙", distinct from the large bottom-right region labeled "丙").
* **Relative Position:**
* The large "甲" region is in the bottom-left part of the large square. The region S₁ is located within this large "甲" region, next to S₃.
* The large "乙" region is in the top-right part of the large square. The region S₂ is located within this large "乙" region, above S₃.
* The large "丙" region is in the bottom-right part of the large square. The smaller central region labeled "丙" is located within this large "丙" region, to the right and below S₃.
* The regions S₁, S₂, S₃, and the smaller central "丙" region are clustered together in the central area of the large square, with S₃ being the central piece surrounded by S₁, S₂, and the central "丙".