200から300の距離値を0から1の範囲にマッピングするC#の関数を以下に示す：
```csharp
float MapDistanceToRange(float distance)
{
    float minDistance = 200.0f;
    float maxDistance = 300.0f;
    float mappedValue = Mathf.InverseLerp(minDistance, maxDistance, distance);
    return mappedValue;
}
```
Mathf.InverseLerp()`関数は最小値と最大値の間の値を0から1の間の正規化された値にマッピングする。この関数は，距離の値を入力として受け取り，マップされた値を返します．

この関数をUnityプロジェクトで使用するには、200と300の間の距離値を指定して呼び出します。例えば

```csharp
float distance = 250.0f;
float mappedValue = MapDistanceToRange(distance);
Debug.Log(mappedValue); // Output: 0.5
```
Here's a function in C# that maps a distance value between 200 and 300 to the range of 0 to 1:
```csharp
float MapDistanceToRange(float distance)
{
    float minDistance = 200.0f;
    float maxDistance = 300.0f;
    float mappedValue = Mathf.InverseLerp(minDistance, maxDistance, distance);
    return mappedValue;
}
```
The `Mathf.InverseLerp()` function maps a value between a minimum and maximum range to a normalized value between 0 and 1. In this example, we set the minimum distance to 200 and the maximum distance to 300. The function takes a distance value as input and returns the mapped value.

You can use this function in your Unity project by calling it with a distance value between 200 and 300. For example:

```csharp
float distance = 250.0f;
float mappedValue = MapDistanceToRange(distance);
Debug.Log(mappedValue); // Output: 0.5
```